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POSTCONF(5)							   POSTCONF(5)

NAME
       postconf - Postfix configuration parameters

SYNOPSIS
       postconf parameter ...

       postconf -e "parameter=value" ...

DESCRIPTION
       The  Postfix main.cf configuration file specifies a small subset of all
       the parameters that control the operation of the Postfix	 mail  system.
       Parameters not specified in main.cf are left at their default values.

       The general format of the main.cf file is as follows:

       ·      Each  logical line has the form "parameter = value".  Whitespace
	      around the "=" is ignored, as is whitespace at the end of a log‐
	      ical line.

       ·      Empty  lines and whitespace-only lines are ignored, as are lines
	      whose first non-whitespace character is a `#'.

       ·      A logical line starts with  non-whitespace  text.	 A  line  that
	      starts with whitespace continues a logical line.

       ·      A parameter value may refer to other parameters.

	      ·	     The  expressions  "$name",	 "${name}"  or	"$(name)"  are
		     recursively replaced by the value of the named parameter.

	      ·	     The expression "${name?value}" expands  to	 "value"  when
		     "$name" is non-empty. This form is supported with Postfix
		     version 2.2 and later.

	      ·	     The expression "${name:value}" expands  to	 "value"  when
		     "$name"  is  empty.  This	form is supported with Postfix
		     version 2.2 and later.

	      ·	     Specify "$$" to produce a single "$" character.

       ·      When the same parameter is defined multiple times, only the last
	      instance is remembered.

       ·      Otherwise,  the  order of main.cf parameter definitions does not
	      matter.

       The remainder of this document is a description of all Postfix configu‐
       ration parameters. Default values are shown after the parameter name in
       parentheses, and can be looked up with the "postconf -d" command.

       Note: this is not an invitation to make changes to  Postfix  configura‐
       tion  parameters.  Unnecessary  changes can impair the operation of the
       mail system.

2bounce_notice_recipient (default: postmaster)
       The recipient of undeliverable mail that	 cannot	 be  returned  to  the
       sender.	This feature is enabled with the notify_classes parameter.

access_map_defer_code (default: 450)
       The  numerical  Postfix	SMTP server response code for an access(5) map
       "defer" action, including "defer_if_permit" or "defer_if_reject". Prior
       to Postfix 2.6, the response is hard-coded as "450".

       Do  not	change	this  unless  you have a complete understanding of RFC
       2821.

       This feature is available in Postfix 2.6 and later.

access_map_reject_code (default: 554)
       The numerical Postfix SMTP server response code for  an	access(5)  map
       "reject" action.

       Do  not	change	this  unless  you have a complete understanding of RFC
       2821.

address_verify_cache_cleanup_interval (default: 12h)
       The amount of time  between  verify(8)  address	verification  database
       cleanup	runs.  This  feature  requires	that the database supports the
       "delete" and "sequence" operators.  Specify a zero interval to  disable
       database cleanup.

       After  each  database cleanup run, the verify(8) daemon logs the number
       of entries that were retained and dropped. A cleanup run is  logged  as
       "partial"  when	the  daemon  terminates	 early after "postfix reload",
       "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.7.

address_verify_default_transport (default: $default_transport)
       Overrides the default_transport parameter setting for address verifica‐
       tion probes.

       This feature is available in Postfix 2.1 and later.

address_verify_local_transport (default: $local_transport)
       Overrides  the  local_transport parameter setting for address verifica‐
       tion probes.

       This feature is available in Postfix 2.1 and later.

address_verify_map (default: see postconf -d output)
       Lookup table for persistent address verification status	storage.   The
       table  is maintained by the verify(8) service, and is opened before the
       process releases privileges.

       The lookup table is persistent by  default  (Postfix  2.7  and  later).
       Specify	an empty table name to keep the information in volatile memory
       which is lost after "postfix reload" or "postfix	 stop".	 This  is  the
       default with Postfix version 2.6 and earlier.

       Specify a location in a file system that will not fill up. If the data‐
       base becomes corrupted, the world comes to an end.  To  recover	delete
       (NOT: truncate) the file and do "postfix reload".

       Postfix	daemon	processes do not use root privileges when opening this
       file (Postfix 2.5 and later).  The file must therefore be stored	 under
       a  Postfix-owned	 directory such as the data_directory.	As a migration
       aid, an attempt to open the file under a non-Postfix directory is redi‐
       rected to the Postfix-owned data_directory, and a warning is logged.

       Examples:

       address_verify_map = hash:/var/lib/postfix/verify
       address_verify_map = btree:/var/lib/postfix/verify

       This feature is available in Postfix 2.1 and later.

address_verify_negative_cache (default: yes)
       Enable caching of failed address verification probe results.  When this
       feature is enabled, the cache may pollute quickly with  garbage.	  When
       this  feature  is  disabled, Postfix will generate an address probe for
       every lookup.

       This feature is available in Postfix 2.1 and later.

address_verify_negative_expire_time (default: 3d)
       The time after which a failed probe expires from the address  verifica‐
       tion cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_negative_refresh_time (default: 3h)
       The  time  after	 which a failed address verification probe needs to be
       refreshed.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_poll_count (default: normal: 3, overload: 1)
       How many times to query the verify(8) service for the completion of  an
       address verification request in progress.

       By  default,  the Postfix SMTP server polls the verify(8) service up to
       three times under non-overload conditions, and  only  once  when	 under
       overload.  With Postfix version 2.5 and earlier, the SMTP server always
       polls the verify(8) service up to three times by default.

       Specify 1 to implement a crude form of  greylisting,  that  is,	always
       defer the first delivery request for a new address.

       Examples:

       # Postfix <= 2.6 default
       address_verify_poll_count = 3
       # Poor man's greylisting
       address_verify_poll_count = 1

       This feature is available in Postfix 2.1 and later.

address_verify_poll_delay (default: 3s)
       The delay between queries for the completion of an address verification
       request in progress.

       The default polling delay is 3 seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_expire_time (default: 31d)
       The time after which a successful probe expires from the address	 veri‐
       fication cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_refresh_time (default: 7d)
       The  time  after which a successful address verification probe needs to
       be refreshed.  The address verification status is not updated when  the
       probe fails (optimistic caching).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_relay_transport (default: $relay_transport)
       Overrides  the  relay_transport parameter setting for address verifica‐
       tion probes.

       This feature is available in Postfix 2.1 and later.

address_verify_relayhost (default: $relayhost)
       Overrides the relayhost	parameter  setting  for	 address  verification
       probes. This information can be overruled with the transport(5) table.

       This feature is available in Postfix 2.1 and later.

address_verify_sender (default: $double_bounce_sender)
       The  sender  address  to	 use  in address verification probes; prior to
       Postfix 2.5 the	default	 was  "postmaster".  To	 avoid	problems  with
       address probes that are sent in response to address probes, the Postfix
       SMTP server excludes the probe sender address  from  all	 SMTPD	access
       blocks.

       Specify	an  empty value (address_verify_sender =) or <> if you want to
       use the null sender address. Beware, some sites reject  mail  from  <>,
       even though RFCs require that such addresses be accepted.

       Examples:

       address_verify_sender = <>
       address_verify_sender = postmaster@my.domain

       This feature is available in Postfix 2.1 and later.

address_verify_sender_dependent_default_transport_maps		     (default:
       $sender_dependent_default_transport_maps)
       Overrides the sender_dependent_default_transport_maps parameter setting
       for address verification probes.

       This feature is available in Postfix 2.7 and later.

address_verify_sender_dependent_relayhost_maps	   (default:	$sender_depen‐
       dent_relayhost_maps)
       Overrides the  sender_dependent_relayhost_maps  parameter  setting  for
       address verification probes.

       This feature is available in Postfix 2.3 and later.

address_verify_service_name (default: verify)
       The  name  of  the verify(8) address verification service. This service
       maintains the status of sender and/or  recipient	 address  verification
       probes, and generates probes on request by other Postfix processes.

address_verify_transport_maps (default: $transport_maps)
       Overrides the transport_maps parameter setting for address verification
       probes.

       This feature is available in Postfix 2.1 and later.

address_verify_virtual_transport (default: $virtual_transport)
       Overrides the virtual_transport parameter setting for address verifica‐
       tion probes.

       This feature is available in Postfix 2.1 and later.

alias_database (default: see postconf -d output)
       The  alias  databases  for  local(8)  delivery  that  are  updated with
       "newaliases" or with "sendmail -bi".

       This is a separate configuration parameter because not all  the	tables
       specified with $alias_maps have to be local files.

       Examples:

       alias_database = hash:/etc/aliases
       alias_database = hash:/etc/mail/aliases

alias_maps (default: see postconf -d output)
       The alias databases that are used for local(8) delivery. See aliases(5)
       for syntax details.

       The default list is system dependent.  On systems with NIS, the default
       is to search the local alias database, then the NIS alias database.

       If  you	change	the  alias  database, run "postalias /etc/aliases" (or
       wherever your system  stores  the  mail	alias  file),  or  simply  run
       "newaliases" to build the necessary DBM or DB file.

       The  local(8)  delivery agent disallows regular expression substitution
       of $1 etc. in alias_maps, because that would open a security hole.

       The local(8) delivery agent will silently ignore requests  to  use  the
       proxymap(8)  server  within  alias_maps. Instead it will open the table
       directly. Before Postfix version 2.2, the local(8) delivery agent  will
       terminate with a fatal error.

       Examples:

       alias_maps = hash:/etc/aliases, nis:mail.aliases
       alias_maps = hash:/etc/aliases

allow_mail_to_commands (default: alias, forward)
       Restrict	 local(8)  mail delivery to external commands.	The default is
       to disallow delivery to "|command" in :include:	files (see  aliases(5)
       for the text that defines this terminology).

       Specify	zero  or more of: alias, forward or include, in order to allow
       commands in aliases(5), .forward files or in :include:  files,  respec‐
       tively.

       Example:

       allow_mail_to_commands = alias,forward,include

allow_mail_to_files (default: alias, forward)
       Restrict	 local(8)  mail	 delivery to external files. The default is to
       disallow "/file/name" destinations in :include:	files (see  aliases(5)
       for the text that defines this terminology).

       Specify	zero  or more of: alias, forward or include, in order to allow
       "/file/name"  destinations  in  aliases(5),  .forward  files   and   in
       :include:  files, respectively.

       Example:

       allow_mail_to_files = alias,forward,include

allow_min_user (default: no)
       Allow a sender or recipient address to have `-' as the first character.
       By default, this is not allowed, to avoid accidents with software  that
       passes email addresses via the command line. Such software would not be
       able to distinguish a malicious address from a bona  fide  command-line
       option.	Although this can be prevented by inserting a "--" option ter‐
       minator into the command line, this is  difficult  to  enforce  consis‐
       tently and globally.

       As  of  Postfix version 2.5, this feature is implemented by trivial-re‐
       write(8).  With	earlier	 versions  this	 feature  was  implemented  by
       qmgr(8) and was limited to recipient addresses only.

allow_percent_hack (default: yes)
       Enable  the rewriting of the form "user%domain" to "user@domain".  This
       is enabled by default.

       Note: with Postfix version 2.2, message header address  rewriting  hap‐
       pens only when one of the following conditions is true:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The  message  is	received  from	a  network client that matches
	      $local_header_rewrite_clients,

       ·      The  message   is	  received   from   the	  network,   and   the
	      remote_header_rewrite_domain  parameter  specifies  a  non-empty
	      value.

       To   get	  the	behavior   before   Postfix   version	2.2,   specify
       "local_header_rewrite_clients = static:all".

       Example:

       allow_percent_hack = no

allow_untrusted_routing (default: no)
       Forward	mail  with sender-specified routing (user[@%!]remote[@%!]site)
       from untrusted clients to destinations matching $relay_domains.

       By default, this feature is turned off.	This closes a nasty open relay
       loophole	 where	a  backup  MX host can be tricked into forwarding junk
       mail to a primary MX host which then spams it out to the world.

       This parameter also controls if non-local addresses with	 sender-speci‐
       fied  routing  can  match  Postfix  access  tables.  By	default,  such
       addresses cannot match Postfix access tables, because  the  address  is
       ambiguous.

alternate_config_directories (default: empty)
       A  list	of  non-default	 Postfix configuration directories that may be
       specified with "-c config_directory" on the command line,  or  via  the
       MAIL_CONFIG environment parameter.

       This list must be specified in the default Postfix configuration direc‐
       tory, and is used by set-gid Postfix commands such as postqueue(1)  and
       postdrop(1).

always_add_missing_headers (default: no)
       Always  add (Resent-) From:, To:, Date: or Message-ID: headers when not
       present.	 Postfix 2.6 and later add these  headers  only	 when  clients
       match  the  local_header_rewrite_clients	 parameter  setting.   Earlier
       Postfix versions always add these headers; this may break  DKIM	signa‐
       tures that cover non-existent headers.

always_bcc (default: empty)
       Optional	 address  that	receives a "blind carbon copy" of each message
       that is received by the Postfix mail system.

       Note: if mail to the BCC address bounces it will	 be  returned  to  the
       sender.

       Note:  automatic	 BCC  recipients  are  produced only for new mail.  To
       avoid mailer loops, automatic BCC recipients are	 not  generated	 after
       Postfix	forwards  mail	internally,  or	 after	Postfix generates mail
       itself.

anvil_rate_time_unit (default: 60s)
       The time unit over which client connection rates and  other  rates  are
       calculated.

       This  feature is implemented by the anvil(8) service which is available
       in Postfix version 2.2 and later.

       The default interval is relatively short. Because of the high frequency
       of updates, the anvil(8) server uses volatile memory only. Thus, infor‐
       mation is lost whenever the process terminates.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

anvil_status_update_time (default: 600s)
       How  frequently	the  anvil(8) connection and rate limiting server logs
       peak usage information.

       This feature is available in Postfix 2.2 and later.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

append_at_myorigin (default: yes)
       With  locally  submitted	 mail,	append the string "@$myorigin" to mail
       addresses without domain information.  With  remotely  submitted	 mail,
       append the string "@$remote_header_rewrite_domain" instead.

       Note  1: this feature is enabled by default and must not be turned off.
       Postfix does not support domain-less addresses.

       Note 2: with Postfix version 2.2, message header address rewriting hap‐
       pens only when one of the following conditions is true:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The  message  is	received  from	a  network client that matches
	      $local_header_rewrite_clients,

       ·      The  message   is	  received   from   the	  network,   and   the
	      remote_header_rewrite_domain  parameter  specifies  a  non-empty
	      value.

       To   get	  the	behavior   before   Postfix   version	2.2,   specify
       "local_header_rewrite_clients = static:all".

append_dot_mydomain (default: yes)
       With   locally  submitted  mail,	 append	 the  string  ".$mydomain"  to
       addresses that have no ".domain" information. With  remotely  submitted
       mail, append the string ".$remote_header_rewrite_domain" instead.

       Note 1: this feature is enabled by default. If disabled, users will not
       be able to send mail to "user@partialdomainname" but will have to spec‐
       ify full domain names instead.

       Note 2: with Postfix version 2.2, message header address rewriting hap‐
       pens only when one of the following conditions is true:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The message is received  from  a	network	 client	 that  matches
	      $local_header_rewrite_clients,

       ·      The   message   is   received   from   the   network,   and  the
	      remote_header_rewrite_domain  parameter  specifies  a  non-empty
	      value.

       To   get	  the	behavior   before   Postfix   version	2.2,   specify
       "local_header_rewrite_clients = static:all".

application_event_drain_time (default: 100s)
       How long the postkick(1) command waits  for  a  request	to  enter  the
       server's input buffer before giving up.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

authorized_flush_users (default: static:anyone)
       List of users who are authorized to flush the queue.

       By default, all users are allowed to flush the queue.  Access is always
       granted if the invoking user is the super-user or the $mail_owner user.
       Otherwise, the real UID of the process is looked up in the system pass‐
       word  file,  and access is granted only if the corresponding login name
       is on the access list.  The username "unknown" is  used	for  processes
       whose real UID is not found in the password file.

       Specify	a  list	 of user names, "/file/name" or "type:table" patterns,
       separated by commas and/or whitespace. The  list	 is  matched  left  to
       right,  and the search stops on the first match. A "/file/name" pattern
       is replaced by its contents; a "type:table"  lookup  table  is  matched
       when  a name matches a lookup key (the lookup result is ignored).  Con‐
       tinue long lines by starting the next  line  with  whitespace.  Specify
       "!pattern"  to  exclude a name from the list. The form "!/file/name" is
       supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_mailq_users (default: static:anyone)
       List of users who are authorized to view the queue.

       By default, all users are allowed to view the queue.  Access is	always
       granted if the invoking user is the super-user or the $mail_owner user.
       Otherwise, the real UID of the process is looked up in the system pass‐
       word  file,  and access is granted only if the corresponding login name
       is on the access list.  The username "unknown" is  used	for  processes
       whose real UID is not found in the password file.

       Specify	a  list	 of user names, "/file/name" or "type:table" patterns,
       separated by commas and/or whitespace. The  list	 is  matched  left  to
       right,  and the search stops on the first match. A "/file/name" pattern
       is replaced by its contents; a "type:table"  lookup  table  is  matched
       when  a name matches a lookup key (the lookup result is ignored).  Con‐
       tinue long lines by starting the next  line  with  whitespace.  Specify
       "!pattern" to exclude a user name from the list. The form "!/file/name"
       is supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_submit_users (default: static:anyone)
       List of users who are authorized to submit mail	with  the  sendmail(1)
       command (and with the privileged postdrop(1) helper command).

       By  default, all users are allowed to submit mail.  Otherwise, the real
       UID of the process is looked up in the system password file, and access
       is  granted only if the corresponding login name is on the access list.
       The username "unknown" is used for processes  whose  real  UID  is  not
       found in the password file. To deny mail submission access to all users
       specify an empty list.

       Specify a list of user names, "/file/name"  or  "type:table"  patterns,
       separated  by  commas  and/or  whitespace.  The list is matched left to
       right, and the search stops on the first match. A "/file/name"  pattern
       is  replaced  by	 its  contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).	  Con‐
       tinue  long  lines  by  starting the next line with whitespace. Specify
       "!pattern" to exclude a user name from the list. The form "!/file/name"
       is supported only in Postfix version 2.4 and later.

       Example:

       authorized_submit_users = !www, static:all

       This feature is available in Postfix 2.2 and later.

authorized_verp_clients (default: $mynetworks)
       What  SMTP clients are allowed to specify the XVERP command.  This com‐
       mand requests that mail be delivered one recipient at a time with a per
       recipient return address.

       By default, only trusted clients are allowed to specify XVERP.

       This  parameter	was introduced with Postfix version 1.1.  Postfix ver‐
       sion 2.1 renamed this parameter	to  smtpd_authorized_verp_clients  and
       changed the default to none.

       Specify	a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the	 network  part
       of a host address. You can also specify hostnames or .domain names (the
       initial	dot  causes  the  domain  to  match  any   name	  below	  it),
       "/file/name"  or	 "type:table"  patterns.   A  "/file/name"  pattern is
       replaced by its contents; a "type:table" lookup table is matched when a
       table  entry  matches  a	 lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace.  Specify
       "!pattern"  to  exclude	an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside	[]  in
       the   authorized_verp_clients   value,  and  in	files  specified  with
       "/file/name".  IP version 6 addresses contain the  ":"  character,  and
       would otherwise be confused with a "type:table" pattern.

backwards_bounce_logfile_compatibility (default: yes)
       Produce	additional bounce(8) logfile records that can be read by Post‐
       fix versions before 2.0. The current and more extensible "name = value"
       format  is  needed in order to implement more sophisticated functional‐
       ity.

       This feature is available in Postfix 2.1 and later.

berkeley_db_create_buffer_size (default: 16777216)
       The per-table I/O buffer size for programs that create Berkeley DB hash
       or btree tables.	 Specify a byte count.

       This feature is available in Postfix 2.0 and later.

berkeley_db_read_buffer_size (default: 131072)
       The  per-table  I/O buffer size for programs that read Berkeley DB hash
       or btree tables.	 Specify a byte count.

       This feature is available in Postfix 2.0 and later.

best_mx_transport (default: empty)
       Where the Postfix SMTP client should deliver mail  when	it  detects  a
       "mail  loops  back  to  myself"	error condition. This happens when the
       local MTA is the best SMTP mail exchanger for a destination not	listed
       in    $mydestination,	$inet_interfaces,   $proxy_interfaces,	 $vir‐
       tual_alias_domains, or $virtual_mailbox_domains.	 By default, the Post‐
       fix SMTP client returns such mail as undeliverable.

       Specify, for example, "best_mx_transport = local" to pass the mail from
       the Postfix SMTP client to the local(8) delivery agent. You can specify
       any message delivery "transport" or "transport:nexthop" that is defined
       in the master.cf file. See the transport(5) manual page for the	syntax
       and meaning of "transport" or "transport:nexthop".

       However,	 this  feature	is expensive because it ties up a Postfix SMTP
       client process while the local(8) delivery agent is doing its work.  It
       is  more	 efficient (for Postfix) to list all hosted domains in a table
       or database.

biff (default: yes)
       Whether or not to use the local biff service.  This service sends  "new
       mail"  notifications  to users who have requested new mail notification
       with the UNIX command "biff y".

       For compatibility reasons this feature is on by	default.   On  systems
       with  lots  of interactive users, the biff service can be a performance
       drain.  Specify "biff = no" in main.cf to disable.

body_checks (default: empty)
       Optional lookup tables for  content  inspection	as  specified  in  the
       body_checks(5) manual page.

       Note: with Postfix versions before 2.0, these rules inspect all content
       after the primary message headers.

body_checks_size_limit (default: 51200)
       How much text in a message body segment (or attachment, if  you	prefer
       to  use	that term) is subjected to body_checks inspection.  The amount
       of text is limited to avoid scanning huge attachments.

       This feature is available in Postfix 2.0 and later.

bounce_notice_recipient (default: postmaster)
       The recipient of postmaster notifications with the message  headers  of
       mail  that Postfix did not deliver and of SMTP conversation transcripts
       of mail that Postfix did not receive.  This feature is enabled with the
       notify_classes parameter.

bounce_queue_lifetime (default: 5d)
       The  maximal  time  a  bounce message is queued before it is considered
       undeliverable.  By default, this is the same as the queue life time for
       regular mail.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is d (days).

       Specify 0 when mail delivery should be tried only once.

       This feature is available in Postfix 2.1 and later.

bounce_service_name (default: bounce)
       The name of the bounce(8) service. This service maintains a  record  of
       failed delivery attempts and generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

bounce_size_limit (default: 50000)
       The  maximal  amount  of	 original  message text that is sent in a non-
       delivery notification. Specify a byte count.  A message is returned  as
       either message/rfc822 (the complete original) or as text/rfc822-headers
       (the headers only).  With Postfix version 2.4 and earlier, a message is
       always  returned as message/rfc822 and is truncated when it exceeds the
       size limit.

       Notes:

       ·      If you  increase	this  limit,  then  you	 should	 increase  the
	      mime_nesting_limit value proportionally.

       ·      Be  careful  when making changes.	 Excessively large values will
	      result in the loss of non-delivery notifications, when a	bounce
	      message size exceeds a local or remote MTA's message size limit.

bounce_template_file (default: empty)
       Pathname	 of a configuration file with bounce message templates.	 These
       override the built-in templates of delivery status  notification	 (DSN)
       messages for undeliverable mail, for delayed mail, successful delivery,
       or delivery verification. The bounce(5) manual page  describes  how  to
       edit and test template files.

       Template message body text may contain $name references to Postfix con‐
       figuration parameters. The result of $name expansion can	 be  previewed
       with "postconf -b file_name" before the file is placed into the Postfix
       configuration directory.

       This feature is available in Postfix 2.3 and later.

broken_sasl_auth_clients (default: no)
       Enable inter-operability with SMTP clients that implement  an  obsolete
       version	of  the	 AUTH command (RFC 4954). Examples of such clients are
       MicroSoft Outlook Express version 4 and MicroSoft Exchange version 5.0.

       Specify "broken_sasl_auth_clients = yes" to have Postfix advertise AUTH
       support in a non-standard way.

canonical_classes      (default:      envelope_sender,	   envelope_recipient,
       header_sender, header_recipient)
       What addresses are  subject  to	canonical_maps	address	 mapping.   By
       default,	 canonical_maps	 address mapping is applied to envelope sender
       and recipient addresses, and to	header	sender	and  header  recipient
       addresses.

       Specify	 one   or   more   of:	 envelope_sender,  envelope_recipient,
       header_sender, header_recipient

       This feature is available in Postfix 2.2 and later.

canonical_maps (default: empty)
       Optional	 address  mapping  lookup  tables  for	message	 headers   and
       envelopes.  The	mapping	 is  applied  to  both	sender	and  recipient
       addresses, in both envelopes and in headers,  as	 controlled  with  the
       canonical_classes  parameter.  This is typically used to clean up dirty
       addresses from legacy mail systems, or to replace login names by First‐
       name.Lastname.	The table format and lookups are documented in canoni‐
       cal(5). For an  overview	 of  Postfix  address  manipulations  see  the
       ADDRESS_REWRITING_README document.

       If you use this feature, run "postmap /usr/local/etc/postfix/canonical"
       to build the necessary DBM or DB file after every change.  The  changes
       will  become  visible  after  a	minute or so.  Use "postfix reload" to
       eliminate the delay.

       Note: with Postfix version 2.2, message header address mapping  happens
       only when message header address rewriting is enabled:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The  message  is	received  from	a  network client that matches
	      $local_header_rewrite_clients,

       ·      The  message   is	  received   from   the	  network,   and   the
	      remote_header_rewrite_domain  parameter  specifies  a  non-empty
	      value.

       To   get	  the	behavior   before   Postfix   version	2.2,   specify
       "local_header_rewrite_clients = static:all".

       Examples:

       canonical_maps = dbm:$config_directory/canonical
       canonical_maps = hash:$config_directory/canonical

cleanup_service_name (default: cleanup)
       The  name  of  the  cleanup(8) service. This service rewrites addresses
       into the standard form, and performs canonical(5) address  mapping  and
       virtual(5) aliasing.

       This feature is available in Postfix 2.0 and later.

command_directory (default: see postconf -d output)
       The location of all postfix administrative commands.

command_execution_directory (default: empty)
       The  local(8) delivery agent working directory for delivery to external
       command.	 Failure  to  change  directory	 causes	 the  delivery	to  be
       deferred.

       The  following $name expansions are done on command_execution_directory
       before the directory is changed. Expansion happens in  the  context  of
       the  delivery  request.	The result of $name expansion is filtered with
       the character set that is specified with the execution_directory_expan‐
       sion_filter parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
	      The full recipient address.

       $extension
	      The optional recipient address extension.

       $domain
	      The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
	      The system-wide recipient address extension delimiter.

       ${name?value}
	      Expands to value when $name is non-empty.

       ${name:value}
	      Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       This feature is available in Postfix 2.2 and later.

command_expansion_filter (default: see postconf -d output)
       Restrict	 the  characters  that	the  local(8) delivery agent allows in
       $name expansions of $mailbox_command and	 $command_execution_directory.
       Characters outside the allowed set are replaced by underscores.

command_time_limit (default: 1000s)
       Time limit for delivery to external commands. This limit is used by the
       local(8) delivery agent, and is the default time limit for delivery  by
       the pipe(8) delivery agent.

       Note:  if  you set this time limit to a large value you must update the
       global ipc_timeout parameter as well.

config_directory (default: see postconf -d output)
       The default location of the Postfix main.cf and master.cf configuration
       files. This can be overruled via the following mechanisms:

       ·      The  MAIL_CONFIG environment variable (daemon processes and com‐
	      mands).

       ·      The "-c" command-line option (commands only).

       With Postfix command that run with set-gid privileges, a	 config_direc‐
       tory  override requires either root privileges, or it requires that the
       directory is listed with the alternate_config_directories parameter  in
       the default main.cf file.

connection_cache_protocol_timeout (default: 5s)
       Time  limit  for	 connection cache connect, send or receive operations.
       The time limit is enforced in the client.

       This feature is available in Postfix 2.3 and later.

connection_cache_service_name (default: scache)
       The name of the scache(8) connection cache service.  This service main‐
       tains a limited pool of cached sessions.

       This feature is available in Postfix 2.2 and later.

connection_cache_status_update_time (default: 600s)
       How  frequently the scache(8) server logs usage statistics with connec‐
       tion cache hit and miss rates for logical destinations and for physical
       endpoints.

connection_cache_ttl_limit (default: 2s)
       The  maximal  time-to-live  value  that	the scache(8) connection cache
       server allows. Requests that specify a larger TTL will be  stored  with
       the  maximum  allowed TTL. The purpose of this additional control is to
       protect the infrastructure against careless people. The	cache  TTL  is
       already bounded by $max_idle.

content_filter (default: empty)
       After  the  message is queued, send the entire message to the specified
       transport:destination. The transport name specifies the first field  of
       a  mail delivery agent definition in master.cf; the syntax of the next-
       hop destination is described in the manual page	of  the	 corresponding
       delivery	 agent.	 More information about external content filters is in
       the Postfix FILTER_README file.

       Notes:

       ·      This setting has lower precedence than a FILTER action  that  is
	      specified	 in  an	 access(5), header_checks(5) or body_checks(5)
	      table.

       ·      The meaning of an empty next-hop filter destination  is  version
	      dependent.  Postfix 2.7 and later will use the recipient domain;
	      earlier versions will use	 $myhostname.	Specify	 "default_fil‐
	      ter_nexthop = $myhostname" for compatibility with Postfix 2.6 or
	      earlier, or specify a  content_filter  value  with  an  explicit
	      next-hop destination.

cyrus_sasl_config_path (default: empty)
       Search  path  for Cyrus SASL application configuration files, currently
       used only to locate the $smtpd_sasl_path.conf file.   Specify  zero  or
       more  directories  separated by a colon character, or an empty value to
       use Cyrus SASL's built-in search path.

       This feature is available in Postfix 2.5 and later when	compiled  with
       Cyrus SASL 2.1.22 or later.

daemon_directory (default: see postconf -d output)
       The directory with Postfix support programs and daemon programs.	 These
       should not be invoked directly by humans. The directory must  be	 owned
       by root.

daemon_timeout (default: 18000s)
       How  much  time	a  Postfix daemon process may take to handle a request
       before it is terminated by a built-in watchdog timer.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

data_directory (default: see postconf -d output)
       The  directory  with  Postfix-writable data files (for example: caches,
       pseudo-random numbers).	This directory must be owned by the mail_owner
       account, and must not be shared with non-Postfix software.

       This feature is available in Postfix 2.5 and later.

debug_peer_level (default: 2)
       The  increment  in verbose logging level when a remote client or server
       matches a pattern in the debug_peer_list parameter.

debug_peer_list (default: empty)
       Optional list of remote client or server hostname  or  network  address
       patterns that cause the verbose logging level to increase by the amount
       specified in $debug_peer_level.

       Specify domain names, network/netmask patterns,	"/file/name"  patterns
       or   "type:table"  lookup  tables.  The	right-hand  side  result  from
       "type:table" lookups is ignored.

       Pattern	matching  of  domain  names  is	  controlled   by   the	  par‐
       ent_domain_matches_subdomains parameter.

       Examples:

       debug_peer_list = 127.0.0.1
       debug_peer_list = example.com

debugger_command (default: empty)
       The  external  command  to  execute  when  a  Postfix daemon program is
       invoked with the -D option.

       Use "command .. & sleep 5" so that the debugger can attach  before  the
       process	marches	 on. If you use an X-based debugger, be sure to set up
       your XAUTHORITY environment variable before starting Postfix.

       Example:

       debugger_command =
	   PATH=/usr/bin:/usr/X11R6/bin
	   ddd $daemon_directory/$process_name $process_id & sleep 5

default_database_type (default: see postconf -d output)
       The default database type for use in  newaliases(1),  postalias(1)  and
       postmap(1)  commands.  On  many UNIX systems the default type is either
       dbm or hash. The default setting is frozen when the Postfix  system  is
       built.

       Examples:

       default_database_type = hash
       default_database_type = dbm

default_delivery_slot_cost (default: 5)
       How  often  the Postfix queue manager's scheduler is allowed to preempt
       delivery of one message with another.

       Each transport maintains a so-called "available delivery slot  counter"
       for  each message. One message can be preempted by another one when the
       other message can be delivered using  no	 more  delivery	 slots	(i.e.,
       invocations  of	delivery  agents) than the current message counter has
       accumulated (or will eventually	accumulate  -  see  about  slot	 loans
       below).	This parameter controls how often is the counter incremented -
       it happens after each default_delivery_slot_cost recipients  have  been
       delivered.

       The  cost of 0 is used to disable the preempting scheduling completely.
       The minimum value the scheduling algorithm can use is 2 - use it if you
       want to maximize the message throughput rate. Although there is no max‐
       imum, it doesn't make much sense to use values above say 50.

       The only reason why the value of 2 is not the default is the  way  this
       parameter affects the delivery of mailing-list mail. In the worst case,
       their  delivery	can   take   somewhere	 between   (cost+1/cost)   and
       (cost/cost-1) times more than if the preemptive scheduler was disabled.
       The default value of 5 turns out to provide reasonable message response
       times while making sure the mailing-list deliveries are not extended by
       more than 20-25 percent even in the worst case.

       Use transport_delivery_slot_cost to specify a transport-specific	 over‐
       ride,  where  transport	is  the master.cf name of the message delivery
       transport.

       Examples:

       default_delivery_slot_cost = 0
       default_delivery_slot_cost = 2

default_delivery_slot_discount (default: 50)
       The default value for transport-specific	 _delivery_slot_discount  set‐
       tings.

       This  parameter speeds up the moment when a message preemption can hap‐
       pen. Instead of	waiting	 until	the  full  amount  of  delivery	 slots
       required	 is available, the preemption can happen when transport_deliv‐
       ery_slot_discount percent of the required amount plus  transport_deliv‐
       ery_slot_loan  still  remains  to  be  accumulated.  Note that the full
       amount will still have to be accumulated before another preemption  can
       take place later.

       Use  transport_delivery_slot_discount  to  specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_delivery_slot_loan (default: 3)
       The default value for transport-specific _delivery_slot_loan settings.

       This  parameter speeds up the moment when a message preemption can hap‐
       pen. Instead of	waiting	 until	the  full  amount  of  delivery	 slots
       required	 is available, the preemption can happen when transport_deliv‐
       ery_slot_discount percent of the required amount plus  transport_deliv‐
       ery_slot_loan  still  remains  to  be  accumulated.  Note that the full
       amount will still have to be accumulated before another preemption  can
       take place later.

       Use  transport_delivery_slot_loan to specify a transport-specific over‐
       ride, where transport is the master.cf name  of	the  message  delivery
       transport.

default_destination_concurrency_failed_cohort_limit (default: 1)
       How  many  pseudo-cohorts  must	suffer connection or handshake failure
       before a specific destination is considered  unavailable	 (and  further
       delivery	 is suspended). Specify zero to disable this feature. A desti‐
       nation's pseudo-cohort failure count is reset each time a delivery com‐
       pletes without connection or handshake failure for that specific desti‐
       nation.

       A pseudo-cohort is the number of deliveries equal  to  a	 destination's
       delivery concurrency.

       Use  transport_destination_concurrency_failed_cohort_limit to specify a
       transport-specific override, where transport is the master.cf  name  of
       the message delivery transport.

       This  feature  is available in Postfix 2.5. The default setting is com‐
       patible with earlier Postfix versions.

default_destination_concurrency_limit (default: 20)
       The default maximal number of parallel deliveries to the same  destina‐
       tion.  This is the default limit for delivery via the lmtp(8), pipe(8),
       smtp(8) and virtual(8) delivery agents.	With per-destination recipient
       limit > 1, a destination is a domain, otherwise it is a recipient.

       Use transport_destination_concurrency_limit to specify a transport-spe‐
       cific override, where transport is the master.cf name  of  the  message
       delivery transport.

default_destination_concurrency_negative_feedback (default: 1)
       The  per-destination  amount of delivery concurrency negative feedback,
       after a delivery completes with	a  connection  or  handshake  failure.
       Feedback	 values	 are  in the range 0..1 inclusive. With negative feed‐
       back, concurrency is decremented at the	beginning  of  a  sequence  of
       length  1/feedback. This is unlike positive feedback, where concurrency
       is incremented at the end of a sequence of length 1/feedback.

       As of Postfix version 2.5, negative  feedback  cannot  reduce  delivery
       concurrency  to	zero.	Instead, a destination is marked dead (further
       delivery	 suspended)  after  the	 failed	 pseudo-cohort	count  reaches
       $default_destination_concurrency_failed_cohort_limit	(or    $trans‐
       port_destination_concurrency_failed_cohort_limit).  To make the	sched‐
       uler  completely	 immune to connection or handshake failures, specify a
       zero feedback value and a zero failed pseudo-cohort limit.

       Specify one of the following forms:

       number

       number / number
	      Constant feedback. The value must be in the  range  0..1	inclu‐
	      sive.   The  default  setting  of "1" is compatible with Postfix
	      versions before 2.5, where a destination's delivery  concurrency
	      is throttled down to zero (and further delivery suspended) after
	      a single failed pseudo-cohort.

       number / concurrency
	      Variable feedback of "number  /  (delivery  concurrency)".   The
	      number must be in the range 0..1 inclusive. With number equal to
	      "1", a destination's delivery concurrency is  decremented	 by  1
	      after each failed pseudo-cohort.

       A  pseudo-cohort	 is  the number of deliveries equal to a destination's
       delivery concurrency.

       Use transport_destination_concurrency_negative_feedback	to  specify  a
       transport-specific  override,  where transport is the master.cf name of
       the message delivery transport.

       This feature is available in Postfix 2.5. The default setting  is  com‐
       patible with earlier Postfix versions.

default_destination_concurrency_positive_feedback (default: 1)
       The  per-destination  amount of delivery concurrency positive feedback,
       after a delivery completes without  connection  or  handshake  failure.
       Feedback	 values	 are  in  the  range  0..1 inclusive.  The concurrency
       increases until it  reaches  the	 per-destination  maximal  concurrency
       limit. With positive feedback, concurrency is incremented at the end of
       a sequence with length 1/feedback. This is  unlike  negative  feedback,
       where  concurrency  is decremented at the start of a sequence of length
       1/feedback.

       Specify one of the following forms:

       number

       number / number
	      Constant feedback.  The value must be in the range  0..1	inclu‐
	      sive. The default setting of "1" is compatible with Postfix ver‐
	      sions before 2.5, where  a  destination's	 delivery  concurrency
	      doubles after each successful pseudo-cohort.

       number / concurrency
	      Variable	feedback  of  "number  / (delivery concurrency)".  The
	      number must be in the range 0..1 inclusive. With number equal to
	      "1",  a  destination's  delivery concurrency is incremented by 1
	      after each successful pseudo-cohort.

       A pseudo-cohort is the number of deliveries equal  to  a	 destination's
       delivery concurrency.

       Use  transport_destination_concurrency_positive_feedback	 to  specify a
       transport-specific override, where transport is the master.cf  name  of
       the message delivery transport.

       This feature is available in Postfix 2.5 and later.

default_destination_rate_delay (default: 0s)
       The  default amount of delay that is inserted between individual deliv‐
       eries to the same destination; with per-destination recipient  limit  >
       1, a destination is a domain, otherwise it is a recipient.

       To  enable  the delay, specify a non-zero time value (an integral value
       plus an optional one-letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       NOTE: the delay is enforced by the queue manager. The delay timer state
       does not survive "postfix reload" or "postfix stop".

       Use transport_destination_rate_delay to	specify	 a  transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       NOTE: with a non-zero _destination_rate_delay, specify a transport_des‐
       tination_concurrency_failed_cohort_limit of 10 or more to prevent Post‐
       fix from deferring all mail for the same	 destination  after  only  one
       connection or handshake error.

       This feature is available in Postfix 2.5 and later.

default_destination_recipient_limit (default: 50)
       The default maximal number of recipients per message delivery.  This is
       the default limit for delivery via the lmtp(8),	pipe(8),  smtp(8)  and
       virtual(8) delivery agents.

       Setting	this parameter to a value of 1 changes the meaning of the cor‐
       responding  per-destination  concurrency	 limit	from  concurrency  per
       domain into concurrency per recipient.

       Use  transport_destination_recipient_limit  to specify a transport-spe‐
       cific override, where transport is the master.cf name  of  the  message
       delivery transport.

default_extra_recipient_limit (default: 1000)
       The default value for the extra per-transport limit imposed on the num‐
       ber of in-memory recipients.  This extra recipient  space  is  reserved
       for  the	 cases when the Postfix queue manager's scheduler preempts one
       message with another and suddenly needs some extra recipients slots for
       the chosen message in order to avoid performance degradation.

       Use  transport_extra_recipient_limit  to	 specify  a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_filter_nexthop (default: empty)
       When  a content_filter or FILTER request specifies no explicit next-hop
       destination, use $default_filter_nexthop instead; when  that  value  is
       empty,  use the domain in the recipient address.	 Specify "default_fil‐
       ter_nexthop = $myhostname" for compatibility with Postfix  version  2.6
       and earlier, or specify an explicit next-hop destination with each con‐
       tent_filter value or FILTER action.

       This feature is available in Postfix 2.7 and later.

default_minimum_delivery_slots (default: 3)
       How many recipients a message must have in order to invoke the  Postfix
       queue  manager's	 scheduling  algorithm	at  all.  Messages which would
       never accumulate at least this many delivery  slots  (subject  to  slot
       cost parameter as well) are never preempted.

       Use  transport_minimum_delivery_slots  to  specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_privs (default: nobody)
       The  default rights used by the local(8) delivery agent for delivery to
       external file or command.  These	 rights	 are  used  when  delivery  is
       requested from an aliases(5) file that is owned by root, or when deliv‐
       ery is done on behalf of root. DO NOT SPECIFY A PRIVILEGED USER OR  THE
       POSTFIX OWNER.

default_process_limit (default: 100)
       The  default  maximal  number of Postfix child processes that provide a
       given service. This limit can be overruled for specific services in the
       master.cf file.

default_rbl_reply (default: see postconf -d output)
       The  default  SMTP  server  response  template  for  a  request that is
       rejected by an RBL-based restriction. This template can be overruled by
       specific entries in the optional rbl_reply_maps lookup table.

       This feature is available in Postfix 2.0 and later.

       The template is subject to exactly one level of $name substitution:

       $client
	      The client hostname and IP address, formatted as name[address].

       $client_address
	      The client IP address.

       $client_name
	      The	client	     hostname	   or	   "unknown".	   See
	      reject_unknown_client_hostname for more details.

       $reverse_client_name
	      The client hostname from	address->name  lookup,	or  "unknown".
	      See reject_unknown_reverse_client_hostname for more details.

       $helo_name
	      The hostname given in HELO or EHLO command or empty string.

       $rbl_class
	      The  blacklisted	entity type: Client host, Helo command, Sender
	      address, or Recipient address.

       $rbl_code
	      The  numerical  SMTP  response  code,  as	 specified  with   the
	      maps_rbl_reject_code  configuration parameter. Note: The numeri‐
	      cal SMTP response code is required, and must appear at the start
	      of  the  reply. With Postfix version 2.3 and later this informa‐
	      tion may be followed by an RFC 3463 enhanced status code.

       $rbl_domain
	      The RBL domain where $rbl_what is blacklisted.

       $rbl_reason
	      The reason why $rbl_what is blacklisted, or an empty string.

       $rbl_what
	      The entity that is blacklisted (an IP  address,  a  hostname,  a
	      domain name, or an email address whose domain was blacklisted).

       $recipient
	      The recipient address or <> in case of the null address.

       $recipient_domain
	      The recipient domain or empty string.

       $recipient_name
	      The recipient address localpart or <> in case of null address.

       $sender
	      The sender address or <> in case of the null address.

       $sender_domain
	      The sender domain or empty string.

       $sender_name
	      The sender address localpart or <> in case of the null address.

       ${name?text}
	      Expands to `text' if $name is not empty.

       ${name:text}
	      Expands to `text' if $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Note:  when  an	enhanced status code is specified in an RBL reply tem‐
       plate, it is subject to modification.   The  following  transformations
       are  needed  when the same RBL reply template is used for client, helo,
       sender, or recipient access restrictions.

       ·      When rejecting a sender address, the Postfix  SMTP  server  will
	      transform	 a  recipient  DSN status (e.g., 4.1.1-4.1.6) into the
	      corresponding sender DSN status, and vice versa.

       ·      When rejecting non-address information (such as the HELO command
	      argument	or  the	 client	 hostname/address),  the  Postfix SMTP
	      server will transform a sender or recipient DSN  status  into  a
	      generic non-address DSN status (e.g., 4.0.0).

default_recipient_limit (default: 20000)
       The default per-transport upper limit on the number of in-memory recip‐
       ients.  These limits take priority over the global qmgr_message_recipi‐
       ent_limit  after the message has been assigned to the respective trans‐
       ports.  See also default_extra_recipient_limit and qmgr_message_recipi‐
       ent_minimum.

       Use transport_recipient_limit to specify a transport-specific override,
       where transport is the master.cf name of the  message  delivery	trans‐
       port.

default_recipient_refill_delay (default: 5s)
       The  default  per-transport  maximum  delay between recipients refills.
       When not all message recipients fit into the memory at once, keep load‐
       ing  more  of them at least once every this many seconds.  This is used
       to make sure the recipients are refilled in  timely  manner  even  when
       $default_recipient_refill_limit is too high for too slow deliveries.

       Use  transport_recipient_refill_delay  to  specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       This feature is available in Postfix 2.4 and later.

default_recipient_refill_limit (default: 100)
       The default per-transport limit on the number of recipients refilled at
       once.  When not all message recipients fit into	the  memory  at	 once,
       keep  loading  more of them in batches of at least this many at a time.
       See also $default_recipient_refill_delay, which may result in recipient
       batches lower than this when this limit is too high for too slow deliv‐
       eries.

       Use transport_recipient_refill_limit to	specify	 a  transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       This feature is available in Postfix 2.4 and later.

default_transport (default: smtp)
       The default mail delivery transport and next-hop destination for desti‐
       nations	 that	do   not   match   $mydestination,   $inet_interfaces,
       $proxy_interfaces, $virtual_alias_domains, $virtual_mailbox_domains, or
       $relay_domains.	  This	 information   can   be	  overruled  with  the
       sender_dependent_default_transport_maps parameter and with  the	trans‐
       port(5) table.

       In  order  of  decreasing  precedence, the nexthop destination is taken
       from   $sender_dependent_default_transport_maps,	   $default_transport,
       $sender_dependent_relayhost_maps,  $relayhost,  or  from	 the recipient
       domain.

       Specify a string of the form transport:nexthop, where transport is  the
       name  of	 a mail delivery transport defined in master.cf.  The :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       Example:

       default_transport = uucp:relayhostname

default_verp_delimiters (default: +=)
       The  two	 default  VERP	delimiter  characters.	These are used when no
       explicit delimiters are specified with the SMTP XVERP command  or  with
       the  "sendmail  -V"  command-line  option.  Specify characters that are
       allowed by the verp_delimiter_filter setting.

       This feature is available in Postfix 1.1 and later.

defer_code (default: 450)
       The numerical Postfix SMTP server response  code	 when  a  remote  SMTP
       client request is rejected by the "defer" restriction.

       Do  not	change	this  unless  you have a complete understanding of RFC
       2821.

defer_service_name (default: defer)
       The name of the defer service.  This  service  is  implemented  by  the
       bounce(8) daemon and maintains a record of failed delivery attempts and
       generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

defer_transports (default: empty)
       The names of message delivery transports that should not	 deliver  mail
       unless someone issues "sendmail -q" or equivalent. Specify zero or more
       names of mail delivery transports names that appear in the first	 field
       of master.cf.

       Example:

       defer_transports = smtp

delay_logging_resolution_limit (default: 2)
       The  maximal number of digits after the decimal point when logging sub-
       second delay values.  Specify a number in the range 0..6.

       Large delay values are rounded off to an integral number seconds; delay
       values  below the delay_logging_resolution_limit are logged as "0", and
       small delay values are logged with at most two-digit precision.

       The format of the "delays=a/b/c/d" logging is as follows:

       ·      a = time from message arrival to last active queue entry

       ·      b = time from last active queue entry to connection setup

       ·      c = time in connection setup, including DNS, EHLO and STARTTLS

       ·      d = time in message transmission

       This feature is available in Postfix 2.3 and later.

delay_notice_recipient (default: postmaster)
       The recipient of postmaster notifications with the message  headers  of
       mail that cannot be delivered within $delay_warning_time time units.

       This feature is enabled with the delay_warning_time parameter.

delay_warning_time (default: 0h)
       The  time  after	 which the sender receives the message headers of mail
       that is still queued.

       To enable this feature, specify a  non-zero  time  value	 (an  integral
       value plus an optional one-letter suffix that specifies the time unit).

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is h (hours).

deliver_lock_attempts (default: 20)
       The maximal number of attempts to acquire an exclusive lock on a	 mail‐
       box file or bounce(8) logfile.

deliver_lock_delay (default: 1s)
       The  time  between  attempts  to acquire an exclusive lock on a mailbox
       file or bounce(8) logfile.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

destination_concurrency_feedback_debug (default: no)
       Make  the  queue	 manager's  feedback algorithm verbose for performance
       analysis purposes.

       This feature is available in Postfix 2.5 and later.

detect_8bit_encoding_header (default: yes)
       Automatically detect 8BITMIME body content by looking at Content-Trans‐
       fer-Encoding:  message  headers;	 historically, this behavior was hard-
       coded to be "always on".

       This feature is available in Postfix 2.5 and later.

disable_dns_lookups (default: no)
       Disable DNS lookups in the Postfix SMTP and  LMTP  clients.  When  dis‐
       abled,  hosts  are looked up with the getaddrinfo() system library rou‐
       tine which normally also looks in /etc/hosts.

       DNS lookups are enabled by default.

disable_mime_input_processing (default: no)
       Turn off MIME processing while receiving mail. This means that no  spe‐
       cial  treatment is given to Content-Type: message headers, and that all
       text after the initial message headers is considered to be part of  the
       message body.

       This feature is available in Postfix 2.0 and later.

       Mime  input processing is enabled by default, and is needed in order to
       recognize MIME headers in message content.

disable_mime_output_conversion (default: no)
       Disable the conversion of 8BITMIME format to 7BIT format.  Mime	output
       conversion  is  needed when the destination does not advertise 8BITMIME
       support.

       This feature is available in Postfix 2.0 and later.

disable_verp_bounces (default: no)
       Disable sending one bounce report per recipient.

       The default, one per recipient, is what ezmlm needs.

       This feature is available in Postfix 1.1 and later.

disable_vrfy_command (default: no)
       Disable the SMTP VRFY command. This stops some techniques used to  har‐
       vest email addresses.

       Example:

       disable_vrfy_command = no

dnsblog_reply_delay (default: 0s)
       A debugging aid to artifically delay DNS responses.

       This feature is available in Postfix 2.8.

dont_remove (default: 0)
       Don't remove queue files and save them to the "saved" mail queue.  This
       is a debugging aid.  To inspect the envelope information and content of
       a Postfix queue file, use the postcat(1) command.

double_bounce_sender (default: double-bounce)
       The  sender  address  of postmaster notifications that are generated by
       the mail system. All mail to this address  is  silently	discarded,  in
       order to terminate mail bounce loops.

duplicate_filter_limit (default: 1000)
       The  maximal  number  of	 addresses remembered by the address duplicate
       filter for aliases(5) or virtual(5) alias expansion,  or	 for  showq(8)
       queue displays.

empty_address_default_transport_maps_lookup_key (default: <;>)
       The  sender_dependent_default_transport_maps search string that will be
       used instead of the null sender address.

       This feature is available in Postfix 2.7 and later.

empty_address_recipient (default: MAILER-DAEMON)
       The recipient of mail addressed to the null address.  Postfix does  not
       accept  such  addresses in SMTP commands, but they may still be created
       locally as the result of configuration or software error.

empty_address_relayhost_maps_lookup_key (default: <;>)
       The sender_dependent_relayhost_maps search string  that	will  be  used
       instead of the null sender address.

       This  feature  is available in Postfix 2.5 and later. With earlier ver‐
       sions, sender_dependent_relayhost_maps lookups  were  skipped  for  the
       null sender address.

enable_errors_to (default: no)
       Report mail delivery errors to the address specified with the non-stan‐
       dard Errors-To: message header, instead of the envelope sender  address
       (this  feature  is  removed  with Postfix version 2.2, is turned off by
       default with Postfix version 2.1, and is always turned  on  with	 older
       Postfix versions).

enable_original_recipient (default: yes)
       Enable  support	for  the  X-Original-To message header. This header is
       needed for multi-recipient mailboxes.

       When this parameter is set  to  yes,  the  cleanup(8)  daemon  performs
       duplicate elimination on distinct pairs of (original recipient, rewrit‐
       ten recipient), and generates non-empty original recipient  queue  file
       records.

       When this parameter is set to no, the cleanup(8) daemon performs dupli‐
       cate elimination on the rewritten recipient address only, and generates
       empty original recipient queue file records.

       This  feature  is available in Postfix 2.1 and later. With Postfix ver‐
       sion 2.0, support for the X-Original-To message header is always turned
       on.  Postfix  versions before 2.0 have no support for the X-Original-To
       message header.

error_notice_recipient (default: postmaster)
       The recipient of postmaster notifications about mail delivery  problems
       that  are  caused  by  policy,  resource,  software or protocol errors.
       These notifications are enabled with the notify_classes parameter.

error_service_name (default: error)
       The name of the error(8) pseudo delivery	 agent.	 This  service	always
       returns mail as undeliverable.

       This feature is available in Postfix 2.0 and later.

execution_directory_expansion_filter (default: see postconf -d output)
       Restrict	 the  characters  that	the  local(8) delivery agent allows in
       $name expansions of $command_execution_directory.   Characters  outside
       the allowed set are replaced by underscores.

       This feature is available in Postfix 2.2 and later.

expand_owner_alias (default: no)
       When  delivering	 to an alias "aliasname" that has an "owner-aliasname"
       companion alias, set the envelope sender address to  the	 expansion  of
       the "owner-aliasname" alias. Normally, Postfix sets the envelope sender
       address to the name of the "owner-aliasname" alias.

export_environment (default: see postconf -d output)
       The list of environment variables that a Postfix process will export to
       non-Postfix  processes. The TZ variable is needed for sane time keeping
       on System-V-ish systems.

       Specify a list of names and/or name=value pairs,	 separated  by	white‐
       space  or  comma. The name=value form is supported with Postfix version
       2.1 and later.

       Example:

       export_environment = TZ PATH=/bin:/usr/bin

extract_recipient_limit (default: 10240)
       The maximal number of recipient addresses  that	Postfix	 will  extract
       from message headers when mail is submitted with "sendmail -t".

       This feature was removed in Postfix version 2.1.

fallback_relay (default: empty)
       Optional	 list of relay hosts for SMTP destinations that can't be found
       or that are unreachable. With Postfix 2.3 this parameter is renamed  to
       smtp_fallback_relay.

       By  default,  mail  is returned to the sender when a destination is not
       found, and delivery is deferred when a destination is unreachable.

       The fallback relays must be SMTP destinations. Specify a domain,	 host,
       host:port,  [host]:port,	 [address]  or [address]:port; the form [host]
       turns off MX lookups.  If you specify multiple SMTP destinations, Post‐
       fix will try them in the specified order.

       Note:  before  Postfix  2.2, do not use the fallback_relay feature when
       relaying mail for a backup  or  primary	MX  domain.  Mail  would  loop
       between	the Postfix MX host and the fallback_relay host when the final
       destination is unavailable.

       ·      In main.cf specify "relay_transport = relay",

       ·      In master.cf specify "-o fallback_relay =" (i.e., empty) at  the
	      end of the relay entry.

       ·      In transport maps, specify "relay:nexthop..."  as the right-hand
	      side for backup or primary MX domain entries.

       Postfix version 2.2 and later will not use the  fallback_relay  feature
       for destinations that it is MX host for.

fallback_transport (default: empty)
       Optional	 message  delivery  transport that the local(8) delivery agent
       should use for names that are not found in the aliases(5) or UNIX pass‐
       word database.

       The  precedence	of  local(8)  delivery	features  from high to low is:
       aliases,	 .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps,  mailbox_command, home_mailbox, mail_spool_direc‐
       tory, fallback_transport_maps, fallback_transport and luser_relay.

fallback_transport_maps (default: empty)
       Optional lookup tables with per-recipient message  delivery  transports
       for  recipients	that the local(8) delivery agent could not find in the
       aliases(5) or UNIX password database.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,	 .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc‐
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       For  safety  reasons, this feature does not allow $number substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

fast_flush_domains (default: $relay_domains)
       Optional list of destinations that  are	eligible  for  per-destination
       logfiles with mail that is queued to those destinations.

       By  default,  Postfix maintains "fast flush" logfiles only for destina‐
       tions that the Postfix SMTP server is willing to	 relay	to  (i.e.  the
       default	  is:	"fast_flush_domains   =	  $relay_domains";   see   the
       relay_domains parameter in the postconf(5) manual).

       Specify a list of hosts or domains, "/file/name" patterns or  "type:ta‐
       ble"  lookup  tables,  separated by commas and/or whitespace.  Continue
       long lines by starting the next line with  whitespace.  A  "/file/name"
       pattern	is  replaced  by  its contents; a "type:table" lookup table is
       matched when the domain or its parent domain appears as lookup key.

       Specify "fast_flush_domains =" (i.e., empty)  to	 disable  the  feature
       altogether.

fast_flush_purge_time (default: 7d)
       The  time  after which an empty per-destination "fast flush" logfile is
       deleted.

       You can specify the time as a number, or as a number followed by a let‐
       ter  that  indicates  the  time	unit:  s=seconds,  m=minutes, h=hours,
       d=days, w=weeks.	 The default time unit is days.

fast_flush_refresh_time (default: 12h)
       The time after which  a	non-empty  but	unread	per-destination	 "fast
       flush"  logfile	needs  to be refreshed.	 The contents of a logfile are
       refreshed by requesting delivery of all messages listed in the logfile.

       You can specify the time as a number, or as a number followed by a let‐
       ter  that  indicates  the  time	unit:  s=seconds,  m=minutes, h=hours,
       d=days, w=weeks.	 The default time unit is hours.

fault_injection_code (default: 0)
       Force specific internal tests to fail, to test the handling  of	errors
       that are difficult to reproduce otherwise.

flush_service_name (default: flush)
       The  name  of the flush(8) service. This service maintains per-destina‐
       tion logfiles with the queue file names of  mail	 that  is  queued  for
       those destinations.

       This feature is available in Postfix 2.0 and later.

fork_attempts (default: 5)
       The maximal number of attempts to fork() a child process.

fork_delay (default: 1s)
       The delay between attempts to fork() a child process.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

forward_expansion_filter (default: see postconf -d output)
       Restrict the characters that the	 local(8)  delivery  agent  allows  in
       $name  expansions of $forward_path.  Characters outside the allowed set
       are replaced by underscores.

forward_path (default: see postconf -d output)
       The local(8) delivery agent search list for  finding  a	.forward  file
       with  user-specified  delivery methods. The first file that is found is
       used.

       The following $name expansions are  done	 on  forward_path  before  the
       search actually happens. The result of $name expansion is filtered with
       the character set that is specified with	 the  forward_expansion_filter
       parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
	      The full recipient address.

       $extension
	      The optional recipient address extension.

       $domain
	      The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
	      The system-wide recipient address extension delimiter.

       ${name?value}
	      Expands to value when $name is non-empty.

       ${name:value}
	      Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Examples:

       forward_path = /var/forward/$user
       forward_path =
	   /var/forward/$user/.forward$recipient_delimiter$extension,
	   /var/forward/$user/.forward

frozen_delivered_to (default: yes)
       Update  the local(8) delivery agent's idea of the Delivered-To: address
       (see prepend_delivered_header) only once, at the start  of  a  delivery
       attempt;	 do  not  update  the  Delivered-To:  address  while expanding
       aliases or .forward files.

       This feature is available in Postfix 2.3 and later. With older  Postfix
       releases,  the behavior is as if this parameter is set to "no". The old
       setting can be expensive with deeply nested aliases or .forward	files.
       When  an	 alias	or .forward file changes the Delivered-To: address, it
       ties up one queue file and one cleanup process instance while  mail  is
       being forwarded.

hash_queue_depth (default: 1)
       The number of subdirectory levels for queue directories listed with the
       hash_queue_names parameter.

       After changing the hash_queue_names or hash_queue_depth parameter, exe‐
       cute the command "postfix reload".

hash_queue_names (default: deferred, defer)
       The names of queue directories that are split across multiple subdirec‐
       tory levels.

       Before Postfix version 2.2, the default list of hashed queues was  sig‐
       nificantly  larger. Claims about improvements in file system technology
       suggest that hashing of the incoming and active	queues	is  no	longer
       needed.	Fewer  hashed  directories speed up the time needed to restart
       Postfix.

       After changing the hash_queue_names or hash_queue_depth parameter, exe‐
       cute the command "postfix reload".

header_address_token_limit (default: 10240)
       The  maximal number of address tokens are allowed in an address message
       header. Information that exceeds the limit is discarded.	 The limit  is
       enforced by the cleanup(8) server.

header_checks (default: empty)
       Optional	 lookup tables for content inspection of primary non-MIME mes‐
       sage headers, as specified in the header_checks(5) manual page.

header_size_limit (default: 102400)
       The maximal amount of memory in bytes for storing a message header.  If
       a  header is larger, the excess is discarded.  The limit is enforced by
       the cleanup(8) server.

helpful_warnings (default: yes)
       Log warnings about  problematic	configuration  settings,  and  provide
       helpful suggestions.

       This feature is available in Postfix 2.0 and later.

home_mailbox (default: empty)
       Optional	 pathname of a mailbox file relative to a local(8) user's home
       directory.

       Specify a pathname ending in "/" for qmail-style delivery.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,	 .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc‐
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       Examples:

       home_mailbox = Mailbox
       home_mailbox = Maildir/

hopcount_limit (default: 50)
       The maximal number of Received:	message headers that is allowed in the
       primary message headers. A message that exceeds the limit  is  bounced,
       in order to stop a mailer loop.

html_directory (default: see postconf -d output)
       The  location of Postfix HTML files that describe how to build, config‐
       ure or operate a specific Postfix subsystem or feature.

ignore_mx_lookup_error (default: no)
       Ignore DNS MX lookups that produce no response.	By default, the	 Post‐
       fix SMTP client defers delivery and tries again after some delay.  This
       behavior is required by the SMTP standard.

       Specify "ignore_mx_lookup_error = yes" to force a DNS A	record	lookup
       instead. This violates the SMTP standard and can result in mis-delivery
       of mail.

import_environment (default: see postconf -d output)
       The list of environment parameters that a Postfix process  will	import
       from a non-Postfix parent process. Examples of relevant parameters:

       TZ     Needed for sane time keeping on most System-V-ish systems.

       DISPLAY
	      Needed for debugging Postfix daemons with an X-windows debugger.

       XAUTHORITY
	      Needed for debugging Postfix daemons with an X-windows debugger.

       MAIL_CONFIG
	      Needed to make "postfix -c" work.

       Specify	a  list	 of names and/or name=value pairs, separated by white‐
       space or comma. The name=value form is supported with  Postfix  version
       2.1 and later.

in_flow_delay (default: 1s)
       Time  to pause before accepting a new message, when the message arrival
       rate exceeds the message delivery rate. This feature is	turned	on  by
       default (it's disabled on SCO UNIX due to an SCO bug).

       With  the  default  100 SMTP server process limit, "in_flow_delay = 1s"
       limits the mail inflow to 100 messages per second above the  number  of
       messages delivered per second.

       Specify 0 to disable the feature. Valid delays are 0..10.

inet_interfaces (default: all)
       The network interface addresses that this mail system receives mail on.
       Specify "all" to receive mail on all network interfaces (default),  and
       "loopback-only"	to  receive  mail  on loopback network interfaces only
       (Postfix version 2.2 and later).	 The parameter also controls  delivery
       of mail to user@[ip.address].

       Note 1: you need to stop and start Postfix when this parameter changes.

       Note 2: address information may be enclosed inside [], but this form is
       not required here.

       When inet_interfaces specifies just one IPv4 and/or IPv6	 address  that
       is  not	a  loopback  address,  the  Postfix  SMTP client will use this
       address as the IP source address for outbound mail. Support for IPv6 is
       available in Postfix version 2.2 and later.

       On  a multi-homed firewall with separate Postfix instances listening on
       the "inside" and "outside" interfaces, this can prevent	each  instance
       from  being  able to reach servers on the "other side" of the firewall.
       Setting smtp_bind_address to 0.0.0.0 avoids the potential  problem  for
       IPv4, and setting smtp_bind_address6 to :: solves the problem for IPv6.

       A better solution for multi-homed firewalls is to leave inet_interfaces
       at the default value and instead use explicit IP addresses in the  mas‐
       ter.cf  SMTP  server  definitions.   This  preserves  the  Postfix SMTP
       client's loop detection, by ensuring that each  side  of	 the  firewall
       knows  that  the	 other	IP  address  is	 still	the same host. Setting
       $inet_interfaces to a single IPv4 and/or IPV6 address is primarily use‐
       ful  with  virtual  hosting  of domains on secondary IP addresses, when
       each IP address serves a different domain (and has a different $myhost‐
       name setting).

       See also the proxy_interfaces parameter, for network addresses that are
       forwarded to Postfix by way of a proxy or address translator.

       Examples:

       inet_interfaces = all (DEFAULT)
       inet_interfaces = loopback-only (Postfix version 2.2 and later)
       inet_interfaces = 127.0.0.1
       inet_interfaces = 127.0.0.1, [::1] (Postfix version 2.2 and later)
       inet_interfaces = 192.168.1.2, 127.0.0.1

inet_protocols (default: ipv4)
       The Internet protocols Postfix will  attempt  to	 use  when  making  or
       accepting  connections.	Specify one or more of "ipv4" or "ipv6", sepa‐
       rated by whitespace or commas. The form "all" is equivalent  to	"ipv4,
       ipv6"  or  "ipv4", depending on whether the operating system implements
       IPv6.

       This feature is available in Postfix 2.2 and later.

       Note: you MUST stop and start Postfix after changing this parameter.

       On systems that pre-date IPV6_V6ONLY support (RFC 3493), an IPv6 server
       will  also  accept  IPv4 connections, even when IPv4 is turned off with
       the inet_protocols parameter.  On  systems  with	 IPV6_V6ONLY  support,
       Postfix	will  use  separate server sockets for IPv6 and IPv4, and each
       will accept only connections for the corresponding protocol.

       When IPv4 support is enabled via the inet_protocols parameter,  Postfix
       will to DNS type A record lookups, and will convert IPv4-in-IPv6 client
       IP addresses (::ffff:1.2.3.4) to their original	IPv4  form  (1.2.3.4).
       The  latter  is	needed on hosts that pre-date IPV6_V6ONLY support (RFC
       3493).

       When IPv6 support is enabled via the inet_protocols parameter,  Postfix
       will do DNS type AAAA record lookups.

       When  both  IPv4	 and IPv6 support are enabled, the Postfix SMTP client
       will attempt to connect via IPv6 before attempting to use IPv4.

       Examples:

       inet_protocols = ipv4 (DEFAULT)
       inet_protocols = all
       inet_protocols = ipv6
       inet_protocols = ipv4, ipv6

initial_destination_concurrency (default: 5)
       The initial per-destination concurrency level for parallel delivery  to
       the same destination.  With per-destination recipient limit > 1, a des‐
       tination is a domain, otherwise it is a recipient.

       Use transport_initial_destination_concurrency to specify	 a  transport-
       specific override, where transport is the master.cf name of the message
       delivery transport (Postfix 2.5 and later).

       Warning: with concurrency of 1, one bad message can be enough to	 block
       all mail to a site.

internal_mail_filter_classes (default: empty)
       What  categories	 of Postfix-generated mail are subject to before-queue
       content inspection by non_smtpd_milters, header_checks and body_checks.
       Specify	zero  or  more	of  the	 following, separated by whitespace or
       comma.

       bounce Inspect the content of delivery status notifications.

       notify Inspect the content of postmaster notifications by  the  smtp(8)
	      and smtpd(8) processes.

       NOTE:  It's generally not safe to enable content inspection of Postfix-
       generated email messages. The user is warned.

       This feature is available in Postfix 2.3 and later.

invalid_hostname_reject_code (default: 501)
       The numerical Postfix SMTP server response code when the client HELO or
       EHLO  command parameter is rejected by the reject_invalid_helo_hostname
       restriction.

       Do not change this unless you have  a  complete	understanding  of  RFC
       2821.

ipc_idle (default: version dependent)
       The  time  after	 which	a client closes an idle internal communication
       channel.	 The purpose is to  allow  servers  to	terminate  voluntarily
       after  they  become  idle.  This	 is  used, for example, by the address
       resolving and rewriting clients.

       With Postfix 2.4 the default value was reduced from 100s to 5s.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

ipc_timeout (default: 3600s)
       The  time  limit	 for sending or receiving information over an internal
       communication channel.  The purpose is to break out of deadlock	situa‐
       tions.  If  the time limit is exceeded the software aborts with a fatal
       error.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

ipc_ttl (default: 1000s)
       The  time  after which a client closes an active internal communication
       channel.	 The purpose is to  allow  servers  to	terminate  voluntarily
       after  reaching	their client limit.  This is used, for example, by the
       address resolving and rewriting clients.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

line_length_limit (default: 2048)
       Upon  input,  long  lines  are  chopped	up into pieces of at most this
       length; upon delivery, long lines are reconstructed.

lmtp_address_preference (default: ipv6)
       The LMTP-specific version of the smtp_address_preference	 configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_assume_final (default: no)
       When  an	 LMTP  server announces no DSN support, assume that the server
       performs final delivery, and send "delivered" delivery status notifica‐
       tions instead of "relayed". The default setting is backwards compatible
       to avoid the infinetisimal possibility of breaking existing  LMTP-based
       content filters.

lmtp_bind_address (default: empty)
       The LMTP-specific version of the smtp_bind_address configuration param‐
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_bind_address6 (default: empty)
       The  LMTP-specific  version  of	the  smtp_bind_address6	 configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_body_checks (default: empty)
       The LMTP-specific version of the smtp_body_checks configuration parame‐
       ter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_cache_connection (default: yes)
       Keep Postfix LMTP client connections open for up to $max_idle  seconds.
       When  the  LMTP	client	receives a request for the same connection the
       connection is reused.

       This parameter is available in Postfix version 2.2 and  earlier.	  With
       Postfix	version	 2.3  and  later, see lmtp_connection_cache_on_demand,
       lmtp_connection_cache_destinations,	 or	   lmtp_connection_re‐
       use_time_limit.

       The  effectiveness of cached connections will be determined by the num‐
       ber of LMTP servers in use, and the concurrency limit specified for the
       LMTP  client.  Cached connections are closed under any of the following
       conditions:

       ·      The LMTP client idle time limit is reached.  This limit is spec‐
	      ified with the Postfix max_idle configuration parameter.

       ·      A	 delivery  request  specifies a different destination than the
	      one currently cached.

       ·      The per-process limit on the  number  of	delivery  requests  is
	      reached.	 This limit is specified with the Postfix max_use con‐
	      figuration parameter.

       ·      Upon the onset of another	 delivery  request,  the  LMTP	server
	      associated with the current session does not respond to the RSET
	      command.

       Most of these limitations will be removed after	Postfix	 implements  a
       connection cache that is shared among multiple LMTP client programs.

lmtp_cname_overrides_servername (default: yes)
       The  LMTP-specific  version of the smtp_cname_overrides_servername con‐
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connect_timeout (default: 0s)
       The LMTP client time limit for completing a  TCP	 connection,  or  zero
       (use the operating system built-in time limit).	When no connection can
       be made within the deadline, the LMTP client tries the next address  on
       the mail exchanger list.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       Example:

       lmtp_connect_timeout = 30s

lmtp_connection_cache_destinations (default: empty)
       The LMTP-specific  version  of  the  smtp_connection_cache_destinations
       configuration parameter.	 See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_on_demand (default: yes)
       The  LMTP-specific  version of the smtp_connection_cache_on_demand con‐
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_time_limit (default: 2s)
       The LMTP-specific version of the smtp_connection_cache_time_limit  con‐
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_reuse_time_limit (default: 300s)
       The  LMTP-specific version of the smtp_connection_reuse_time_limit con‐
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_data_done_timeout (default: 600s)
       The LMTP client time limit for sending the LMTP ".", and for  receiving
       the server response.  When no response is received within the deadline,
       a warning is logged that the mail may be delivered multiple times.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_data_init_timeout (default: 120s)
       The  LMTP  client time limit for sending the LMTP DATA command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_data_xfer_timeout (default: 180s)
       The  LMTP client time limit for sending the LMTP message content.  When
       the connection stalls for more than  $lmtp_data_xfer_timeout  the  LMTP
       client terminates the transfer.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_defer_if_no_mx_address_found (default: no)
       The LMTP-specific version of the smtp_defer_if_no_mx_address_found con‐
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_destination_concurrency_limit    (default:	  $default_destination_concur‐
       rency_limit)
       The maximal number of parallel deliveries to the same  destination  via
       the  lmtp  message  delivery  transport.	 This limit is enforced by the
       queue manager. The message delivery transport name is the  first	 field
       in the entry in the master.cf file.

lmtp_destination_recipient_limit     (default:	  $default_destination_recipi‐
       ent_limit)
       The maximal number of recipients	 per  message  for  the	 lmtp  message
       delivery	 transport.  This  limit is enforced by the queue manager. The
       message delivery transport name is the first field in the entry in  the
       master.cf file.

       Setting this parameter to a value of 1 changes the meaning of lmtp_des‐
       tination_concurrency_limit from concurrency per domain into concurrency
       per recipient.

lmtp_discard_lhlo_keyword_address_maps (default: empty)
       Lookup  tables,	indexed	 by  the remote LMTP server address, with case
       insensitive lists of LHLO keywords (pipelining, starttls,  auth,	 etc.)
       that  the  LMTP	client	will ignore in the LHLO response from a remote
       LMTP server. See lmtp_discard_lhlo_keywords for details. The  table  is
       not  indexed  by	 hostname for consistency with smtpd_discard_ehlo_key‐
       word_address_maps.

       This feature is available in Postfix 2.3 and later.

lmtp_discard_lhlo_keywords (default: empty)
       A case insensitive list of LHLO keywords (pipelining,  starttls,	 auth,
       etc.)  that  the	 LMTP  client  will ignore in the LHLO response from a
       remote LMTP server.

       This feature is available in Postfix 2.3 and later.

       Notes:

       ·      Specify the silent-discard pseudo keyword to prevent this action
	      from being logged.

       ·      Use  the	lmtp_discard_lhlo_keyword_address_maps feature to dis‐
	      card LHLO keywords selectively.

lmtp_dns_resolver_options (default: empty)
       The LMTP-specific version of the	 smtp_dns_resolver_options  configura‐
       tion parameter.	See there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_enforce_tls (default: no)
       The LMTP-specific version of the smtp_enforce_tls configuration parame‐
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_generic_maps (default: empty)
       The LMTP-specific version of the smtp_generic_maps configuration param‐
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_header_checks (default: empty)
       The  LMTP-specific  version  of	the  smtp_header_checks	 configuration
       parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_host_lookup (default: dns)
       The LMTP-specific version of the smtp_host_lookup configuration parame‐
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_name (default: $myhostname)
       The hostname to send in the LMTP LHLO command.

       The  default  value  is	the  machine  hostname.	 Specify a hostname or
       [ip.add.re.ss].

       This information can be specified in the	 main.cf  file	for  all  LMTP
       clients,	 or  it	 can be specified in the master.cf file for a specific
       client, for example:

	   /usr/local/etc/postfix/master.cf:
	       mylmtp ... lmtp -o lmtp_lhlo_name=foo.bar.com

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_timeout (default: 300s)
       The LMTP client time limit  for	sending	 the  LHLO  command,  and  for
       receiving the initial server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_line_length_limit (default: 990)
       The LMTP-specific version of the	 smtp_line_length_limit	 configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mail_timeout (default: 300s)
       The  LMTP  client time limit for sending the MAIL FROM command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_mime_header_checks (default: empty)
       The  LMTP-specific version of the smtp_mime_header_checks configuration
       parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_mx_address_limit (default: 5)
       The LMTP-specific version of  the  smtp_mx_address_limit	 configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mx_session_limit (default: 2)
       The  LMTP-specific  version  of the smtp_mx_session_limit configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_nested_header_checks (default: empty)
       The LMTP-specific version of the	 smtp_nested_header_checks  configura‐
       tion parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_pix_workaround_delay_time (default: 10s)
       The LMTP-specific version of the smtp_pix_workaround_delay_time config‐
       uration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workaround_maps (default: empty)
       The LMTP-specific version of the smtp_pix_workaround_maps configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.4 and later.

lmtp_pix_workaround_threshold_time (default: 500s)
       The  LMTP-specific  version  of	the smtp_pix_workaround_threshold_time
       configuration parameter.	 See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workarounds (default: empty)
       The LMTP-specific  version  of  the  smtp_pix_workaround	 configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.4 and later.

lmtp_quit_timeout (default: 300s)
       The  LMTP  client  time	limit  for  sending  the QUIT command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_quote_rfc821_envelope (default: yes)
       The  LMTP-specific version of the smtp_quote_rfc821_envelope configura‐
       tion parameter.	See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_randomize_addresses (default: yes)
       The LMTP-specific version of the smtp_randomize_addresses configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_rcpt_timeout (default: 300s)
       The  LMTP  client  time	limit for sending the RCPT TO command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_reply_filter (default: empty)
       The LMTP-specific version of the smtp_reply_filter configuration param‐
       eter.  See there for details.

       This feature is available in Postfix 2.7 and later.

lmtp_rset_timeout (default: 20s)
       The LMTP client time limit  for	sending	 the  RSET  command,  and  for
       receiving  the  server response. The LMTP client sends RSET in order to
       finish a recipient address probe, or to verify that a cached connection
       is still alive.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_sasl_auth_cache_name (default: empty)
       The LMTP-specific version of the	 smtp_sasl_auth_cache_name  configura‐
       tion parameter.	See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_cache_time (default: 90d)
       The  LMTP-specific  version of the smtp_sasl_auth_cache_time configura‐
       tion parameter.	See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix LMTP client.

lmtp_sasl_auth_soft_bounce (default: yes)
       The LMTP-specific version of the smtp_sasl_auth_soft_bounce  configura‐
       tion parameter.	See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_mechanism_filter (default: empty)
       The  LMTP-specific version of the smtp_sasl_mechanism_filter configura‐
       tion parameter.	See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_password_maps (default: empty)
       Optional LMTP client lookup tables with one username:password entry per
       host  or	 domain.   If a remote host or domain has no username:password
       entry, then the Postfix LMTP client will not attempt to authenticate to
       the remote host.

lmtp_sasl_path (default: empty)
       Implementation-specific	information that is passed through to the SASL
       plug-in implementation that is selected with lmtp_sasl_type.  Typically
       this specifies the name of a configuration file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_security_options (default: noplaintext, noanonymous)
       SASL security options; as of Postfix 2.3 the list of available features
       depends on  the	SASL  client  implementation  that  is	selected  with
       lmtp_sasl_type.

       The  following  security features are defined for the cyrus client SASL
       implementation:

       noplaintext
	      Disallow authentication methods that use plaintext passwords.

       noactive
	      Disallow authentication methods that are vulnerable to  non-dic‐
	      tionary active attacks.

       nodictionary
	      Disallow	authentication	methods that are vulnerable to passive
	      dictionary attack.

       noanonymous
	      Disallow anonymous logins.

       Example:

       lmtp_sasl_security_options = noplaintext

lmtp_sasl_tls_security_options (default: $lmtp_sasl_security_options)
       The LMTP-specific version of the smtp_sasl_tls_security_options config‐
       uration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_tls_verified_security_options	    (default:	  $lmtp_sasl_tls_secu‐
       rity_options)
       The   LMTP-specific   version   of   the	  smtp_sasl_tls_verified_secu‐
       rity_options configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_type (default: cyrus)
       The  SASL  plug-in  type	 that  the  Postfix LMTP client should use for
       authentication.	The available types are listed with the "postconf  -A"
       command.

       This feature is available in Postfix 2.3 and later.

lmtp_send_xforward_command (default: no)
       Send  an	 XFORWARD command to the LMTP server when the LMTP LHLO server
       response announces XFORWARD support.  This allows an  lmtp(8)  delivery
       agent,  used for content filter message injection, to forward the name,
       address, protocol and HELO name of the original client to  the  content
       filter and downstream queuing LMTP server.  Before you change the value
       to yes, it is best to make sure that your content filter supports  this
       command.

       This feature is available in Postfix 2.1 and later.

lmtp_sender_dependent_authentication (default: no)
       The  LMTP-specific  version of the smtp_sender_dependent_authentication
       configuration parameter.	 See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_5xx_greeting (default: yes)
       The LMTP-specific version of the	 smtp_skip_5xx_greeting	 configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_quit_response (default: no)
       Wait for the response to the LMTP QUIT command.

lmtp_starttls_timeout (default: 300s)
       The  LMTP-specific  version  of the smtp_starttls_timeout configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tcp_port (default: 24)
       The default TCP port that the Postfix LMTP client connects to.

lmtp_tls_CAfile (default: empty)
       The LMTP-specific version of the smtp_tls_CAfile configuration  parame‐
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_CApath (default: empty)
       The  LMTP-specific version of the smtp_tls_CApath configuration parame‐
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_block_early_mail_reply (default: empty)
       The LMTP-specific version of the	 smtp_tls_block_early_mail_reply  con‐
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.7 and later.

lmtp_tls_cert_file (default: empty)
       The  LMTP-specific  version  of	the  smtp_tls_cert_file	 configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_ciphers (default: export)
       The LMTP-specific version of the smtp_tls_ciphers configuration parame‐
       ter. See there for details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_dcert_file (default: empty)
       The  LMTP-specific  version  of	the  smtp_tls_dcert_file configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_dkey_file (default: $lmtp_tls_dcert_file)
       The  LMTP-specific  version  of	the  smtp_tls_dkey_file	 configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_eccert_file (default: empty)
       The  LMTP-specific  version  of	the smtp_tls_eccert_file configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.6 and  later,  when  Postfix  is
       compiled and linked with OpenSSL 1.0.0 or later.

lmtp_tls_eckey_file (default: empty)
       The  LMTP-specific  version  of	the  smtp_tls_eckey_file configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.6 and  later,  when  Postfix  is
       compiled and linked with OpenSSL 1.0.0 or later.

lmtp_tls_enforce_peername (default: yes)
       The  LMTP-specific  version of the smtp_tls_enforce_peername configura‐
       tion parameter.	See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_exclude_ciphers (default: empty)
       The LMTP-specific version of the smtp_tls_exclude_ciphers configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_fingerprint_cert_match (default: empty)
       The  LMTP-specific  version of the smtp_tls_fingerprint_cert_match con‐
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_fingerprint_digest (default: md5)
       The LMTP-specific version of the smtp_tls_fingerprint_digest configura‐
       tion parameter.	See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_key_file (default: $lmtp_tls_cert_file)
       The LMTP-specific version of the smtp_tls_key_file configuration param‐
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_loglevel (default: 0)
       The LMTP-specific version of the smtp_tls_loglevel configuration param‐
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_ciphers (default: empty)
       The  LMTP-specific version of the smtp_tls_mandatory_ciphers configura‐
       tion parameter.	See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_exclude_ciphers (default: empty)
       The LMTP-specific  version  of  the  smtp_tls_mandatory_exclude_ciphers
       configuration parameter.	 See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_protocols (default: SSLv3, TLSv1)
       The  LMTP-specific version of the smtp_tls_mandatory_protocols configu‐
       ration parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_note_starttls_offer (default: no)
       The LMTP-specific version of the smtp_tls_note_starttls_offer  configu‐
       ration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_per_site (default: empty)
       The LMTP-specific version of the smtp_tls_per_site configuration param‐
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_policy_maps (default: empty)
       The LMTP-specific version  of  the  smtp_tls_policy_maps	 configuration
       parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_protocols (default: empty)
       The  LMTP-specific  version  of	the  smtp_tls_protocols	 configuration
       parameter. See there for details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_scert_verifydepth (default: 9)
       The LMTP-specific version of the smtp_tls_scert_verifydepth  configura‐
       tion parameter.	See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_secure_cert_match (default: nexthop)
       The  LMTP-specific version of the smtp_tls_secure_cert_match configura‐
       tion parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_security_level (default: empty)
       The LMTP-specific version of the smtp_tls_security_level	 configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_database (default: empty)
       The  LMTP-specific  version of the smtp_tls_session_cache_database con‐
       figuration parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_timeout (default: 3600s)
       The LMTP-specific version of the smtp_tls_session_cache_timeout config‐
       uration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_verify_cert_match (default: hostname)
       The  LMTP-specific version of the smtp_tls_verify_cert_match configura‐
       tion parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_use_tls (default: no)
       The LMTP-specific version of the smtp_use_tls configuration  parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_xforward_timeout (default: 300s)
       The  LMTP  client  time limit for sending the XFORWARD command, and for
       receiving the server response.

       In case of problems the client does NOT try the	next  address  on  the
       mail exchanger list.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

local_command_shell (default: empty)
       Optional shell program for local(8) delivery  to	 non-Postfix  command.
       By  default,  non-Postfix  commands are executed directly; commands are
       given to given to the default shell (typically, /bin/sh) only when they
       contain shell meta characters or shell built-in commands.

       "sendmail's  restricted	shell" (smrsh) is what most people will use in
       order to restrict what programs can be run  from	 e.g.  .forward	 files
       (smrsh is part of the Sendmail distribution).

       Note:  when  a  shell program is specified, it is invoked even when the
       command contains no shell built-in commands or meta characters.

       Example:

       local_command_shell = /some/where/smrsh -c
       local_command_shell = /bin/bash -c

local_destination_concurrency_limit (default: 2)
       The maximal number of parallel deliveries via the local	mail  delivery
       transport   to  the  same  recipient  (when  "local_destination_recipi‐
       ent_limit = 1") or the maximal number of	 parallel  deliveries  to  the
       same  local domain (when "local_destination_recipient_limit > 1"). This
       limit is enforced by the queue manager. The message delivery  transport
       name is the first field in the entry in the master.cf file.

       A  low limit of 2 is recommended, just in case someone has an expensive
       shell command in a .forward file or in an alias (e.g., a	 mailing  list
       manager).  You don't want to run lots of those at the same time.

local_destination_recipient_limit (default: 1)
       The  maximal  number  of	 recipients per message delivery via the local
       mail delivery transport. This limit is enforced by the  queue  manager.
       The  message delivery transport name is the first field in the entry in
       the master.cf file.

       Setting this parameter to a value > 1 changes the meaning of local_des‐
       tination_concurrency_limit  from concurrency per recipient into concur‐
       rency per domain.

local_header_rewrite_clients (default: permit_inet_interfaces)
       Rewrite message header addresses in mail from these clients and	update
       incomplete  addresses  with  the domain name in $myorigin or $mydomain;
       either don't rewrite message headers from other clients at all, or  re‐
       write  message  headers and update incomplete addresses with the domain
       specified in the remote_header_rewrite_domain parameter.

       See  the	 append_at_myorigin  and  append_dot_mydomain  parameters  for
       details of how domain names are appended to incomplete addresses.

       Specify a list of zero or more of the following:

       permit_inet_interfaces
	      Append the domain name in $myorigin or $mydomain when the client
	      IP address matches $inet_interfaces. This is enabled by default.

       permit_mynetworks
	      Append the domain name in $myorigin or $mydomain when the client
	      IP  address  matches  any	 network  or network address listed in
	      $mynetworks. This setting will not prevent  remote  mail	header
	      address rewriting when mail from a remote client is forwarded by
	      a neighboring system.

       permit_sasl_authenticated
	      Append the domain name in $myorigin or $mydomain when the client
	      is successfully authenticated via the RFC 4954 (AUTH) protocol.

       permit_tls_clientcerts
	      Append the domain name in $myorigin or $mydomain when the client
	      TLS certificate fingerprint  is  listed  in  $relay_clientcerts.
	      The   fingerprint	 digest	 algorithm  is	configurable  via  the
	      smtpd_tls_fingerprint_digest parameter (hard-coded as md5	 prior
	      to Postfix version 2.5).

       permit_tls_all_clientcerts
	      Append the domain name in $myorigin or $mydomain when the client
	      TLS certificate is successfully verified, regardless of  whether
	      it  is  listed  on  the server, and regardless of the certifying
	      authority.

       check_address_map type:table

       type:table
	      Append the domain name in $myorigin or $mydomain when the client
	      IP  address  matches  the	 specified  lookup  table.  The lookup
	      result is ignored, and no subnet lookup is done. This  is	 suit‐
	      able for, e.g., pop-before-smtp lookup tables.

       Examples:

       The  Postfix < 2.2 backwards compatible setting: always rewrite message
       headers,	 and  always  append  my  own  domain  to  incomplete	header
       addresses.

	   local_header_rewrite_clients = static:all

       The  purist  (and  default)  setting: rewrite headers only in mail from
       Postfix sendmail and in SMTP mail from this machine.

	   local_header_rewrite_clients = permit_inet_interfaces

       The intermediate setting: rewrite header addresses and append $myorigin
       or  $mydomain  information  only	 with mail from Postfix sendmail, from
       local clients, or from authorized SMTP clients.

       Note: this setting will not prevent remote mail header address  rewrit‐
       ing  when  mail from a remote client is forwarded by a neighboring sys‐
       tem.

	   local_header_rewrite_clients = permit_mynetworks,
	       permit_sasl_authenticated permit_tls_clientcerts
	       check_address_map hash:$config_directory/pop-before-smtp

local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps)
       Lookup tables with all names or addresses of local recipients: a recip‐
       ient   address	is  local  when	 its  domain  matches  $mydestination,
       $inet_interfaces or $proxy_interfaces.  Specify @domain as a  wild-card
       for  domains  that  do  not  have a valid recipient list.  Technically,
       tables listed with $local_recipient_maps are  used  as  lists:  Postfix
       needs  to know only if a lookup string is found or not, but it does not
       use the result from table lookup.

       If this parameter is non-empty (the default),  then  the	 Postfix  SMTP
       server will reject mail for unknown local users.

       To  turn off local recipient checking in the Postfix SMTP server, spec‐
       ify "local_recipient_maps =" (i.e. empty).

       The default setting assumes that you  use  the  default	Postfix	 local
       delivery agent for local delivery. You need to update the local_recipi‐
       ent_maps setting if:

       ·      You redefine the local delivery agent in master.cf.

       ·      You redefine the "local_transport" setting in main.cf.

       ·      You  use	the  "luser_relay",  "mailbox_transport",  or	"fall‐
	      back_transport" feature of the Postfix local(8) delivery agent.

       Details are described in the LOCAL_RECIPIENT_README file.

       Beware:	if  the	 Postfix SMTP server runs chrooted, you need to access
       the passwd file via the	proxymap(8)  service,  in  order  to  overcome
       chroot  access restrictions. The alternative, maintaining a copy of the
       system password file in the chroot jail is not practical.

       Examples:

       local_recipient_maps =

local_transport (default: local:$myhostname)
       The default mail delivery transport and next-hop destination for	 final
       delivery to domains listed with mydestination, and for [ipaddress] des‐
       tinations  that	match  $inet_interfaces	 or  $proxy_interfaces.	  This
       information can be overruled with the transport(5) table.

       By  default,  local  mail is delivered to the transport called "local",
       which is just the name of a service that is defined the master.cf file.

       Specify a string of the form transport:nexthop, where transport is  the
       name  of	 a mail delivery transport defined in master.cf.  The :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       Beware:	if you override the default local delivery agent then you need
       to review  the  LOCAL_RECIPIENT_README  document,  otherwise  the  SMTP
       server may reject mail for local recipients.

luser_relay (default: empty)
       Optional	 catch-all  destination	 for  unknown local(8) recipients.  By
       default, mail for unknown recipients in domains that match  $mydestina‐
       tion,  $inet_interfaces	or $proxy_interfaces is returned as undeliver‐
       able.

       The following $name expansions are done on luser_relay:

       $domain
	      The recipient domain.

       $extension
	      The recipient address extension.

       $home  The recipient's home directory.

       $local The entire recipient address localpart.

       $recipient
	      The full recipient address.

       $recipient_delimiter
	      The system-wide recipient address extension delimiter.

       $shell The recipient's login shell.

       $user  The recipient username.

       ${name?value}
	      Expands to value when $name has a non-empty value.

       ${name:value}
	      Expands to value when $name has an empty value.

       Instead of $name you can also specify ${name} or $(name).

       Note: luser_relay works only for the Postfix local(8) delivery agent.

       Note: if you use this feature for accounts not  in  the	UNIX  password
       file,  then  you	 must specify "local_recipient_maps =" (i.e. empty) in
       the main.cf file, otherwise the Postfix SMTP server  will  reject  mail
       for non-UNIX accounts with "User unknown in local recipient table".

       Examples:

       luser_relay = $user@other.host
       luser_relay = $local@other.host
       luser_relay = admin+$local

mail_name (default: Postfix)
       The  mail  system  name	that is displayed in Received: headers, in the
       SMTP greeting banner, and in bounced mail.

mail_owner (default: postfix)
       The UNIX system account that owns the Postfix queue  and	 most  Postfix
       daemon  processes.   Specify  the  name of a user account that does not
       share a group with other accounts and that owns no other files or  pro‐
       cesses  on  the system.	In particular, don't specify nobody or daemon.
       PLEASE USE A DEDICATED USER ID AND GROUP ID.

       When this parameter value is changed you need to re-run	"postfix  set-
       permissions"	(with	  Postfix    version	2.0    and    earlier:
       "/usr/local/etc/postfix/post-install set-permissions".

mail_release_date (default: see postconf -d output)
       The Postfix release date, in "YYYYMMDD" format.

mail_spool_directory (default: see postconf -d output)
       The directory where local(8) UNIX-style mailboxes are kept. The default
       setting	depends	 on  the  system  type. Specify a name ending in / for
       maildir-style delivery.

       Note: maildir delivery is done with the privileges  of  the  recipient.
       If you use the mail_spool_directory setting for maildir style delivery,
       then you must create the top-level maildir directory in advance.	 Post‐
       fix will not create it.

       Examples:

       mail_spool_directory = /var/mail
       mail_spool_directory = /var/spool/mail

mail_version (default: see postconf -d output)
       The   version   of   the	  mail	 system.  Stable  releases  are	 named
       major.minor.patchlevel. Experimental releases also include the  release
       date. The version string can be used in, for example, the SMTP greeting
       banner.

mailbox_command (default: empty)
       Optional external command that the local(8) delivery agent  should  use
       for mailbox delivery.  The command is run with the user ID and the pri‐
       mary group ID privileges of the recipient.  Exception: command delivery
       for  root executes with $default_privs privileges.  This is not a prob‐
       lem, because 1) mail for root should always be aliased to a  real  user
       and 2) don't log in as root, use "su" instead.

       The following environment variables are exported to the command:

       CLIENT_ADDRESS
	      Remote  client network address. Available in Postfix version 2.2
	      and later.

       CLIENT_HELO
	      Remote client EHLO command parameter. Available in Postfix  ver‐
	      sion 2.2 and later.

       CLIENT_HOSTNAME
	      Remote  client  hostname.	 Available  in Postfix version 2.2 and
	      later.

       CLIENT_PROTOCOL
	      Remote client protocol. Available in  Postfix  version  2.2  and
	      later.

       DOMAIN The domain part of the recipient address.

       EXTENSION
	      The optional address extension.

       HOME   The recipient home directory.

       LOCAL  The recipient address localpart.

       LOGNAME
	      The recipient's username.

       ORIGINAL_RECIPIENT
	      The  entire  recipient  address, before any address rewriting or
	      aliasing.

       RECIPIENT
	      The full recipient address.

       SASL_METHOD
	      SASL authentication method specified in the remote  client  AUTH
	      command. Available in Postfix version 2.2 and later.

       SASL_SENDER
	      SASL  sender  address  specified	in the remote client MAIL FROM
	      command. Available in Postfix version 2.2 and later.

       SASL_USER
	      SASL username specified  in  the	remote	client	AUTH  command.
	      Available in Postfix version 2.2 and later.

       SENDER The full sender address.

       SHELL  The recipient's login shell.

       USER   The recipient username.

       Unlike  other  Postfix  configuration  parameters,  the mailbox_command
       parameter is not subjected to $name substitutions. This is to  make  it
       easier to specify shell syntax (see example below).

       If you can, avoid shell meta characters because they will force Postfix
       to run an expensive shell process. If you're  delivering	 via  Procmail
       then  running  a	 shell won't make a noticeable difference in the total
       cost.

       Note: if you use the mailbox_command feature to	deliver	 mail  system-
       wide,  you  must	 set up an alias that forwards mail for root to a real
       user.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,	 .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc‐
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       Examples:

       mailbox_command = /some/where/procmail
       mailbox_command = /some/where/procmail -a "$EXTENSION"
       mailbox_command = /some/where/maildrop -d "$USER"
	       -f "$SENDER" "$EXTENSION"

mailbox_command_maps (default: empty)
       Optional	 lookup tables with per-recipient external commands to use for
       local(8) mailbox delivery.  Behavior is as with mailbox_command.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,	 .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc‐
       tory, fallback_transport_maps, fallback_transport and luser_relay.

mailbox_delivery_lock (default: see postconf -d output)
       How  to	lock a UNIX-style local(8) mailbox before attempting delivery.
       For a list of available file locking methods,  use  the	"postconf  -l"
       command.

       This  setting  is  ignored  with	 maildir  style delivery, because such
       deliveries are safe without explicit locks.

       Note: The dotlock method requires that the recipient  UID  or  GID  has
       write access to the parent directory of the mailbox file.

       Note: the default setting of this parameter is system dependent.

mailbox_size_limit (default: 51200000)
       The maximal size of any local(8) individual mailbox or maildir file, or
       zero (no limit).	 In fact, this limits the size of  any	file  that  is
       written	to  upon  local	 delivery, including files written by external
       commands that are executed by the local(8) delivery agent.

       This limit must not be smaller than the message size limit.

mailbox_transport (default: empty)
       Optional message delivery transport that the  local(8)  delivery	 agent
       should use for mailbox delivery to all local recipients, whether or not
       they are found in the UNIX passwd database.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,	 .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc‐
       tory, fallback_transport_maps, fallback_transport and luser_relay.

mailbox_transport_maps (default: empty)
       Optional	 lookup	 tables with per-recipient message delivery transports
       to use for local(8) mailbox delivery, whether or not the recipients are
       found in the UNIX passwd database.

       The  precedence	of  local(8)  delivery	features  from high to low is:
       aliases,	 .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps,  mailbox_command, home_mailbox, mail_spool_direc‐
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       For safety reasons, this feature does not allow	$number	 substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

mailq_path (default: see postconf -d output)
       Sendmail	  compatibility	 feature  that	specifies  where  the  Postfix
       mailq(1) command is installed. This command can be  used	 to  list  the
       Postfix mail queue.

manpage_directory (default: see postconf -d output)
       Where the Postfix manual pages are installed.

maps_rbl_domains (default: empty)
       Obsolete feature: use the reject_rbl_client feature instead.

maps_rbl_reject_code (default: 554)
       The  numerical  Postfix	SMTP  server  response code when a remote SMTP
       client	 request    is	  blocked    by	    the	    reject_rbl_client,
       reject_rhsbl_client,  reject_rhsbl_reverse_client,  reject_rhsbl_sender
       or reject_rhsbl_recipient restriction.

       Do not change this unless you have  a  complete	understanding  of  RFC
       2821.

masquerade_classes (default: envelope_sender, header_sender, header_recipient)

       What addresses are subject to address masquerading.

       By  default,  address  masquerading  is	limited	 to  envelope	sender
       addresses,  and	to header sender and header recipient addresses.  This
       allows you to use address masquerading on a mail	 gateway  while	 still
       being able to forward mail to users on individual machines.

       Specify	 zero	or   more   of:	 envelope_sender,  envelope_recipient,
       header_sender, header_recipient

masquerade_domains (default: empty)
       Optional list of domains whose subdomain structure will be stripped off
       in email addresses.

       The  list is processed left to right, and processing stops at the first
       match.  Thus,

	   masquerade_domains = foo.example.com example.com

       strips "user@any.thing.foo.example.com" to "user@foo.example.com",  but
       strips "user@any.thing.else.example.com" to "user@example.com".

       A  domain  name	prefixed with ! means do not masquerade this domain or
       its subdomains. Thus,

	   masquerade_domains = !foo.example.com example.com

       does not	 change	 "user@any.thing.foo.example.com"  or  "user@foo.exam‐
       ple.com",  but  strips "user@any.thing.else.example.com" to "user@exam‐
       ple.com".

       Note: with Postfix version 2.2,	message	 header	 address  masquerading
       happens only when message header address rewriting is enabled:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The  message  is	received  from	a  network client that matches
	      $local_header_rewrite_clients,

       ·      The  message   is	  received   from   the	  network,   and   the
	      remote_header_rewrite_domain  parameter  specifies  a  non-empty
	      value.

       To   get	  the	behavior   before   Postfix   version	2.2,   specify
       "local_header_rewrite_clients = static:all".

       Example:

       masquerade_domains = $mydomain

masquerade_exceptions (default: empty)
       Optional	 list  of  user	 names	that are not subjected to address mas‐
       querading, even when their address matches $masquerade_domains.

       By default, address masquerading makes no exceptions.

       Specify a list of user names, "/file/name"  or  "type:table"  patterns,
       separated  by  commas  and/or  whitespace.  The list is matched left to
       right, and the search stops on the first match. A "/file/name"  pattern
       is  replaced  by	 its  contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).	  Con‐
       tinue  long  lines  by  starting the next line with whitespace. Specify
       "!pattern" to exclude a name from the list. The form  "!/file/name"  is
       supported only in Postfix version 2.4 and later.

       Examples:

       masquerade_exceptions = root, mailer-daemon
       masquerade_exceptions = root

master_service_disable (default: empty)
       Selectively disable master(8) listener ports by service type or by ser‐
       vice name and type.  Specify a list of service types  ("inet",  "unix",
       "fifo",	or  "pass")  or	 "name.type" tuples, where "name" is the first
       field of a master.cf entry and "type" is a service type. As with	 other
       Postfix	matchlists, a search stops at the first match.	Specify "!pat‐
       tern" to exclude a service from the list.  By  default,	all  master(8)
       listener ports are enabled.

       Note:  this  feature does not support "/file/name" or "type:table" pat‐
       terns, nor does it support wildcards such as  "*"  or  "all".  This  is
       intentional.

       Examples:

       # Turn on all master(8) listener ports (the default).
       master_service_disable =
       # Turn off only the main SMTP listener port.
       master_service_disable = smtp.inet
       # Turn off all TCP/IP listener ports.
       master_service_disable = inet
       # Turn off all TCP/IP listener ports except "foo".
       master_service_disable = !foo.inet, inet

       This feature is available in Postfix 2.6 and later.

max_idle (default: 100s)
       The  maximum  amount  of time that an idle Postfix daemon process waits
       for an incoming connection before terminating voluntarily.  This param‐
       eter  is	 ignored  by the Postfix queue manager and by other long-lived
       Postfix daemon processes.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

max_use (default: 100)
       The  maximal  number  of	 incoming  connections	that  a Postfix daemon
       process will service before terminating voluntarily.  This parameter is
       ignored	by  the	 Postfix queue manager and by other long-lived Postfix
       daemon processes.

maximal_backoff_time (default: 4000s)
       The maximal time between attempts to deliver a deferred message.

       This parameter should be set to a value greater than or equal to $mini‐
       mal_backoff_time. See also $queue_run_delay.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

maximal_queue_lifetime (default: 5d)
       The maximal time a message is queued before it is sent back as undeliv‐
       erable.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is d (days).

       Specify 0 when mail delivery should be tried only once.

message_reject_characters (default: empty)
       The set of characters that Postfix will reject in message content.  The
       usual C-like escape sequences are recognized: \a \b \f \n \r \t \v \ddd
       (up to three octal digits) and \\.

       Example:

       message_reject_characters = \0

       This feature is available in Postfix 2.3 and later.

message_size_limit (default: 10240000)
       The maximal size in bytes of a message, including envelope information.

       Note: be careful when making changes.  Excessively  small  values  will
       result in the loss of non-delivery notifications, when a bounce message
       size exceeds the local or remote MTA's message size limit.

message_strip_characters (default: empty)
       The set of characters that Postfix will remove  from  message  content.
       The  usual C-like escape sequences are recognized: \a \b \f \n \r \t \v
       \ddd (up to three octal digits) and \\.

       Example:

       message_strip_characters = \0

       This feature is available in Postfix 2.3 and later.

milter_command_timeout (default: 30s)
       The time limit for sending an SMTP command to a	Milter	(mail  filter)
       application, and for receiving the response.

       Specify	a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_connect_macros (default: see postconf -d output)
       The  macros  that  are  sent to Milter (mail filter) applications after
       completion of an SMTP connection.  See  MILTER_README  for  a  list  of
       available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_connect_timeout (default: 30s)
       The  time  limit	 for connecting to a Milter (mail filter) application,
       and for negotiating protocol options.

       Specify a non-zero time value (an integral value plus an optional  one-
       letter suffix that specifies the time unit).

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_content_timeout (default: 300s)
       The time limit for sending message content to a	Milter	(mail  filter)
       application, and for receiving the response.

       Specify	a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_data_macros (default: see postconf -d output)
       The  macros  that  are sent to version 4 or higher Milter (mail filter)
       applications after the SMTP DATA command. See MILTER_README for a  list
       of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_default_action (default: tempfail)
       The  default action when a Milter (mail filter) application is unavail‐
       able or mis-configured. Specify one of the following:

       accept Proceed as if the mail filter was not present.

       reject Reject all further commands in this  session  with  a  permanent
	      status code.

       tempfail
	      Reject  all  further  commands  in this session with a temporary
	      status code.

       quarantine
	      Like "accept", but freeze	 the  message  in  the	"hold"	queue.
	      Available with Postfix 2.6 and later.

       This feature is available in Postfix 2.3 and later.

milter_end_of_data_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       message end-of-data. See MILTER_README for a list  of  available	 macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_end_of_header_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       end of the message header. See MILTER_README for a  list	 of  available
       macro names and their meanings.

       This feature is available in Postfix 2.5 and later.

milter_header_checks (default: empty)
       Optional	 lookup	 tables for content inspection of message headers that
       are produced by Milter applications.  See the  header_checks(5)	manual
       page available actions. Currently, PREPEND is not implemented.

       The  following  example sends all mail that is marked as SPAM to a spam
       handling machine. Note that matches are case-insensitive by default.

       /usr/local/etc/postfix/main.cf:
	   milter_header_checks = pcre:$config_directory/milter_header_checks

       /usr/local/etc/postfix/milter_header_checks:
	   /^X-SPAM-FLAG:\s+YES/ FILTER mysmtp:sanitizer.example.com:25

       The milter_header_checks mechanism could also be used for whitelisting.
       For example it could be used to skip heavy content inspection for DKIM-
       signed mail from known friendly domains.

       This feature is available in Postfix 2.7, and as an optional patch  for
       Postfix 2.6.

milter_helo_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP HELO or EHLO command. See MILTER_README for a  list	 of  available
       macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_macro_daemon_name (default: $myhostname)
       The  {daemon_name}  macro  value for Milter (mail filter) applications.
       See MILTER_README for a list of available macro names and  their	 mean‐
       ings.

       This feature is available in Postfix 2.3 and later.

milter_macro_v (default: $mail_name $mail_version)
       The  {v}	 macro	value for Milter (mail filter) applications.  See MIL‐
       TER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_mail_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP MAIL FROM command. See MILTER_README for a list of available macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_protocol (default: 6)
       The mail filter protocol version and optional protocol  extensions  for
       communication  with  a  Milter  application;  prior  to Postfix 2.6 the
       default protocol is 2. Postfix sends this  version  number  during  the
       initial protocol handshake.  It should match the version number that is
       expected by the mail filter application (or by its Milter library).

       Protocol versions:

       2      Use Sendmail 8 mail filter  protocol  version  2	(default  with
	      Sendmail version 8.11 .. 8.13 and Postfix version 2.3 ..	2.5).

       3      Use Sendmail 8 mail filter protocol version 3.

       4      Use Sendmail 8 mail filter protocol version 4.

       6      Use  Sendmail  8	mail  filter  protocol version 6 (default with
	      Sendmail version 8.14 and Postfix version 2.6).

       Protocol extensions:

       no_header_reply
	      Specify this when the Milter application will not reply for each
	      individual message header.

       This feature is available in Postfix 2.3 and later.

milter_rcpt_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP RCPT TO command. See MILTER_README for a list of  available	 macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_unknown_command_macros (default: see postconf -d output)
       The  macros  that  are sent to version 3 or higher Milter (mail filter)
       applications after an unknown SMTP command.  See	 MILTER_README	for  a
       list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

mime_boundary_length_limit (default: 2048)
       The maximal length of MIME multipart boundary strings. The MIME proces‐
       sor is unable to distinguish between boundary strings that do not  dif‐
       fer in the first $mime_boundary_length_limit characters.

       This feature is available in Postfix 2.0 and later.

mime_header_checks (default: $header_checks)
       Optional	 lookup	 tables for content inspection of MIME related message
       headers, as described in the header_checks(5) manual page.

       This feature is available in Postfix 2.0 and later.

mime_nesting_limit (default: 100)
       The maximal recursion level that the MIME processor will handle.	 Post‐
       fix refuses mail that is nested deeper than the specified limit.

       This feature is available in Postfix 2.0 and later.

minimal_backoff_time (default: 300s)
       The  minimal time between attempts to deliver a deferred message; prior
       to Postfix 2.4 the default value was 1000s.

       This parameter also limits the time an unreachable destination is  kept
       in the short-term, in-memory, destination status cache.

       This parameter should be set greater than or equal to $queue_run_delay.
       See also $maximal_backoff_time.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

multi_instance_directories (default: empty)
       An  optional  list  of  non-default  Postfix configuration directories;
       these directories belong to additional Postfix instances that share the
       Postfix	executable  files  and	documentation with the default Postfix
       instance, and that  are	started,  stopped,  etc.,  together  with  the
       default	Postfix	 instance.   Specify  a list of pathnames separated by
       comma or whitespace.

       When $multi_instance_directories is empty, the postfix(1) command  runs
       in single-instance mode and operates on a single Postfix instance only.
       Otherwise, the postfix(1)  command  runs	 in  multi-instance  mode  and
       invokes	  the	 multi-instance	   manager    specified	   with	   the
       multi_instance_wrapper parameter. The multi-instance  manager  in  turn
       executes postfix(1) commands for the default instance and for all Post‐
       fix instances in $multi_instance_directories.

       Currently, this parameter setting is ignored  except  for  the  default
       main.cf file.

       This feature is available in Postfix 2.6 and later.

multi_instance_enable (default: no)
       Allow  this  Postfix instance to be started, stopped, etc., by a multi-
       instance manager.  By default, new instances  are  created  in  a  safe
       state that prevents them from being started inadvertently.  This param‐
       eter is reserved for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_group (default: empty)
       The optional instance group name of  this  Postfix  instance.  A	 group
       identifies  closely-related  Postfix  instances that the multi-instance
       manager can start, stop, etc., as a unit.  This parameter  is  reserved
       for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_name (default: empty)
       The  optional instance name of this Postfix instance. This name becomes
       also the default value for the syslog_name parameter.

       This feature is available in Postfix 2.6 and later.

multi_instance_wrapper (default: empty)
       The pathname of a multi-instance manager command	 that  the  postfix(1)
       command	invokes when the multi_instance_directories parameter value is
       non-empty. The pathname may be followed by  initial  command  arguments
       separated  by  whitespace;  shell metacharacters such as quotes are not
       supported in this context.

       The postfix(1) command invokes the manager command with the  postfix(1)
       non-option  command arguments on the manager command line, and with all
       installation configuration parameters exported into the manager command
       process environment. The manager command in turn invokes the postfix(1)
       command for individual Postfix instances as "postfix  -c	 config_direc‐
       tory command".

       This feature is available in Postfix 2.6 and later.

multi_recipient_bounce_reject_code (default: 550)
       The  numerical  Postfix	SMTP  server  response code when a remote SMTP
       client request is blocked by the reject_multi_recipient_bounce restric‐
       tion.

       Do  not	change	this  unless  you have a complete understanding of RFC
       2821.

       This feature is available in Postfix 2.1 and later.

mydestination (default: $myhostname, localhost.$mydomain, localhost)
       The list of domains that are delivered via  the	$local_transport  mail
       delivery	 transport.  By	 default this is the Postfix local(8) delivery
       agent which looks up all recipients in  /etc/passwd  and	 /etc/aliases.
       The  SMTP  server  validates  recipient	addresses  with $local_recipi‐
       ent_maps and rejects non-existent recipients. See also the local domain
       class in the ADDRESS_CLASS_README file.

       The  default  mydestination value specifies names for the local machine
       only.  On a mail domain gateway, you should also include $mydomain.

       The  $local_transport  delivery	method	is  also  selected  for	  mail
       addressed  to  user@[the.net.work.address]  of  the mail system (the IP
       addresses  specified  with  the	inet_interfaces	 and  proxy_interfaces
       parameters).

       Warnings:

       ·      Do  not specify the names of virtual domains - those domains are
	      specified elsewhere. See VIRTUAL_README for more information.

       ·      Do not specify the names of domains that this machine is	backup
	      MX host for. See STANDARD_CONFIGURATION_README for how to set up
	      backup MX hosts.

       ·      By default, the Postfix SMTP server rejects mail for  recipients
	      not  listed  with	 the  local_recipient_maps parameter.  See the
	      postconf(5) manual for a description of the local_recipient_maps
	      and unknown_local_recipient_reject_code parameters.

       Specify	a  list	 of host or domain names, "/file/name" or "type:table"
       patterns, separated by commas and/or whitespace. A "/file/name" pattern
       is  replaced  by	 its  contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).	  Con‐
       tinue long lines by starting the next line with whitespace.

       Examples:

       mydestination = $myhostname, localhost.$mydomain $mydomain
       mydestination = $myhostname, localhost.$mydomain www.$mydomain, ftp.$mydomain

mydomain (default: see postconf -d output)
       The  internet  domain  name of this mail system.	 The default is to use
       $myhostname minus the first component, or  "localdomain"	 (Postfix  2.3
       and  later).   $mydomain is used as a default value for many other con‐
       figuration parameters.

       Example:

       mydomain = domain.tld

myhostname (default: see postconf -d output)
       The internet hostname of this mail system. The default is  to  use  the
       fully-qualified	domain	name  (FQDN) from gethostname(), or to use the
       non-FQDN result from gethostname() and append  ".$mydomain".   $myhost‐
       name  is	 used  as a default value for many other configuration parame‐
       ters.

       Example:

       myhostname = host.example.com

mynetworks (default: see postconf -d output)
       The list of "trusted" SMTP  clients  that  have	more  privileges  than
       "strangers".

       In particular, "trusted" SMTP clients are allowed to relay mail through
       Postfix.	 See the smtpd_recipient_restrictions parameter description in
       the postconf(5) manual.

       You  can specify the list of "trusted" network addresses by hand or you
       can let Postfix do it for you (which is the default).  See the descrip‐
       tion of the mynetworks_style parameter for more information.

       If  you specify the mynetworks list by hand, Postfix ignores the mynet‐
       works_style setting.

       Specify a list of network addresses or network/netmask patterns,	 sepa‐
       rated  by commas and/or whitespace. Continue long lines by starting the
       next line with whitespace.

       The netmask specifies the number of bits in the network part of a  host
       address.	  You  can also specify "/file/name" or "type:table" patterns.
       A "/file/name" pattern is replaced  by  its  contents;  a  "type:table"
       lookup table is matched when a table entry matches a lookup string (the
       lookup result is ignored).

       The list is matched left to right, and the search stops	on  the	 first
       match.	Specify "!pattern" to exclude an address or network block from
       the list. The form "!/file/name" is supported only in  Postfix  version
       2.4 and later.

       Note:  IP  version 6 address information must be specified inside [] in
       the mynetworks value, and in files  specified  with  "/file/name".   IP
       version	6  addresses contain the ":" character, and would otherwise be
       confused with a "type:table" pattern.

       Examples:

       mynetworks = 127.0.0.0/8 168.100.189.0/28
       mynetworks = !192.168.0.1, 192.168.0.0/28
       mynetworks = 127.0.0.0/8 168.100.189.0/28 [::1]/128 [2001:240:587::]/64
       mynetworks = $config_directory/mynetworks
       mynetworks = hash:$config_directory/network_table

mynetworks_style (default: subnet)
       The method to generate the default value for the mynetworks  parameter.
       This is the list of trusted networks for relay access control etc.

       ·      Specify  "mynetworks_style  =  host" when Postfix should "trust"
	      only the local machine.

       ·      Specify "mynetworks_style = subnet" when Postfix should  "trust"
	      SMTP  clients  in	 the same IP subnetworks as the local machine.
	      On Linux, this works correctly only  with	 interfaces  specified
	      with the "ifconfig" command.

       ·      Specify  "mynetworks_style  = class" when Postfix should "trust"
	      SMTP clients in the same IP class A/B/C networks	as  the	 local
	      machine.	 Don't	do  this  with	a dialup site - it would cause
	      Postfix to "trust" your  entire  provider's  network.   Instead,
	      specify  an  explicit mynetworks list by hand, as described with
	      the mynetworks configuration parameter.

myorigin (default: $myhostname)
       The domain name that locally-posted mail appears to come from, and that
       locally	posted mail is delivered to. The default, $myhostname, is ade‐
       quate for small sites.  If you run a domain with multiple machines, you
       should  (1) change this to $mydomain and (2) set up a domain-wide alias
       database that aliases each user to user@that.users.mailhost.

       Example:

       myorigin = $mydomain

nested_header_checks (default: $header_checks)
       Optional lookup tables for content inspection of non-MIME message head‐
       ers  in	attached messages, as described in the header_checks(5) manual
       page.

       This feature is available in Postfix 2.0 and later.

newaliases_path (default: see postconf -d output)
       Sendmail compatibility feature  that  specifies	the  location  of  the
       newaliases(1) command. This command can be used to rebuild the local(8)
       aliases(5) database.

non_fqdn_reject_code (default: 504)
       The numerical Postfix SMTP server reply code when a client  request  is
       rejected	 by  the reject_non_fqdn_helo_hostname, reject_non_fqdn_sender
       or reject_non_fqdn_recipient restriction.

non_smtpd_milters (default: empty)
       A list of Milter (mail filter) applications for new mail that does  not
       arrive  via the Postfix smtpd(8) server. This includes local submission
       via the sendmail(1) command line, new mail that arrives via the Postfix
       qmqpd(8)	 server,  and old mail that is re-injected into the queue with
       "postsuper -r".	See the MILTER_README document for details.

       This feature is available in Postfix 2.3 and later.

notify_classes (default: resource, software)
       The list of error classes that are  reported  to	 the  postmaster.  The
       default	is  to report only the most serious problems. The paranoid may
       wish to turn on the policy (UCE and mail relaying) and  protocol	 error
       (broken mail software) reports.

       NOTE:  postmaster  notifications	 may  contain confidential information
       such as SASL passwords or message content.  It is the  system  adminis‐
       trator's responsibility to treat such information with care.

       The error classes are:

       bounce (also implies 2bounce)
	      Send  the	 postmaster copies of the headers of bounced mail, and
	      send transcripts of SMTP sessions when Postfix rejects mail. The
	      notification   is	  sent	to  the	 address  specified  with  the
	      bounce_notice_recipient configuration parameter (default:	 post‐
	      master).

       2bounce
	      Send undeliverable bounced mail to the postmaster. The notifica‐
	      tion   is	  sent	 to   the   address   specified	   with	   the
	      2bounce_notice_recipient configuration parameter (default: post‐
	      master).

       delay  Send the postmaster copies of the headers of delayed  mail.  The
	      notification   is	  sent	to  the	 address  specified  with  the
	      delay_notice_recipient configuration parameter  (default:	 post‐
	      master).

       policy Send  the	 postmaster  a	transcript  of the SMTP session when a
	      client request was rejected because of (UCE) policy. The notifi‐
	      cation   is   sent   to	the   address	specified   with   the
	      error_notice_recipient configuration parameter  (default:	 post‐
	      master).

       protocol
	      Send  the postmaster a transcript of the SMTP session in case of
	      client or server protocol errors. The notification  is  sent  to
	      the address specified with the error_notice_recipient configura‐
	      tion parameter (default: postmaster).

       resource
	      Inform the postmaster of mail  not  delivered  due  to  resource
	      problems.	  The  notification  is	 sent to the address specified
	      with   the   error_notice_recipient   configuration    parameter
	      (default: postmaster).

       software
	      Inform  the  postmaster  of  mail	 not delivered due to software
	      problems.	 The notification is sent  to  the  address  specified
	      with    the   error_notice_recipient   configuration   parameter
	      (default: postmaster).

       Examples:

       notify_classes = bounce, delay, policy, protocol, resource, software
       notify_classes = 2bounce, resource, software

owner_request_special (default: yes)
       Give special treatment to owner-listname and  listname-request  address
       localparts:  don't split such addresses when the recipient_delimiter is
       set to "-".  This feature is useful for mailing lists.

parent_domain_matches_subdomains (default: see postconf -d output)
       What Postfix features match subdomains of  "domain.tld"	automatically,
       instead	of  requiring  an  explicit  ".domain.tld"  pattern.   This is
       planned backwards compatibility:	 eventually, all Postfix features  are
       expected	 to  require  explicit	".domain.tld"  style patterns when you
       really want to match subdomains.

permit_mx_backup_networks (default: empty)
       Restrict the use of the permit_mx_backup SMTP access  feature  to  only
       domains	whose primary MX hosts match the listed networks.  The parame‐
       ter value syntax is the same as with the	 mynetworks  parameter;	 note,
       however, that the default value is empty.

pickup_service_name (default: pickup)
       The  name  of  the  pickup(8) service. This service picks up local mail
       submissions from the Postfix maildrop queue.

       This feature is available in Postfix 2.0 and later.

plaintext_reject_code (default: 450)
       The numerical Postfix SMTP server  response  code  when	a  request  is
       rejected by the reject_plaintext_session restriction.

       This feature is available in Postfix 2.3 and later.

postmulti_control_commands (default: reload flush)
       The  postfix(1)	commands that the postmulti(1) instance manager treats
       as "control" commands, that operate on  running	instances.  For	 these
       commands, disabled instances are skipped.

       This feature is available in Postfix 2.6 and later.

postmulti_start_commands (default: start)
       The  postfix(1)	commands that the postmulti(1) instance manager treats
       as  "start"  commands.  For  these  commands,  disabled	instances  are
       "checked"  rather  than	"started",  and	 failure  to  "start" a member
       instance of  an	instance  group	 will  abort  the  start-up  of	 later
       instances.

       This feature is available in Postfix 2.6 and later.

postmulti_stop_commands (default: see postconf -d output)
       The  postfix(1)	commands that the postmulti(1) instance manager treats
       as "stop" commands. For these commands, disabled instances are skipped,
       and enabled instances are processed in reverse order.

       This feature is available in Postfix 2.6 and later.

postscreen_bare_newline_action (default: ignore)
       The  action  that  postscreen(8) takes when an SMTP client sends a bare
       newline character, that is, a newline not preceded by carriage  return.
       Specify one of the following:

       ignore Ignore  the failure of this test. Allow other tests to complete.
	      Do not repeat this test before some the result from  some	 other
	      test  expires.  This option is useful for testing and collecting
	      statistics without blocking mail permanently.

       enforce
	      Allow other tests to complete. Reject attempts to	 deliver  mail
	      with  a 550 SMTP reply, and log the helo/sender/recipient infor‐
	      mation.  Repeat this test the next time the client connects.

       drop   Drop the connection immediately with a 521  SMTP	reply.	Repeat
	      this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_enable (default: no)
       Enable  "bare newline" SMTP protocol tests in the postscreen(8) server.
       These tests are expensive: a client must disconnect after it passes the
       test, before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_ttl (default: 30d)
       The  amount  of	time that postscreen(8) will cache results from a suc‐
       cessful "bare newline" SMTP protocol test. During this time, the client
       IP  address  is	excluded from this test. The default is long because a
       client must disconnect after it passes the test, before it can talk  to
       a real Postfix SMTP server.

       Specify	a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).  Time units: s  (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_blacklist_action (default: ignore)
       The  action that postscreen(8) takes when an SMTP client is permanently
       blacklisted with the postscreen_blacklist_networks parameter.   Specify
       one of the following:

       ignore (default)
	      Ignore  this result. Allow other tests to complete.  Repeat this
	      test the next time the client connects.  This option  is	useful
	      for testing and collecting statistics without blocking mail.

       enforce
	      Allow  other  tests to complete. Reject attempts to deliver mail
	      with a 550 SMTP reply, and log the helo/sender/recipient	infor‐
	      mation.  Repeat this test the next time the client connects.

       drop   Drop  the	 connection  immediately with a 521 SMTP reply. Repeat
	      this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_blacklist_networks (default: empty)
       Network	addresses  that	  are	permanently   blacklisted;   see   the
       postscreen_blacklist_action   parameter	for  possible  actions.	  This
       parameter uses the same address syntax  as  the	mynetworks  parameter.
       The blacklist has higher precedence than whitelists. This feature never
       uses the remote SMTP client hostname.

       This feature is available in Postfix 2.8.

postscreen_cache_cleanup_interval (default: 12h)
       The amount of time between postscreen(8)	 cache	cleanup	 runs.	 Cache
       cleanup	increases  the load on the cache database and should therefore
       not be run frequently. This feature requires that  the  cache  database
       supports	 the "delete" and "sequence" operators.	 Specify a zero inter‐
       val to disable cache cleanup.

       After each cache cleanup run, the postscreen(8) daemon logs the	number
       of  entries  that were retained and dropped. A cleanup run is logged as
       "partial" when the daemon  terminates  early  after  "postfix  reload",
       "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_cache_map (default: btree:$data_directory/ps_cache)
       Persistent storage for the postscreen(8) server decisions.

       This feature is available in Postfix 2.8.

postscreen_cache_retention_time (default: 7d)
       The  amount  of time that postscreen(8) will cache an expired temporary
       whitelist entry before it is removed. This prevents clients from	 being
       logged  as "NEW" just because their cache entry expired an hour ago. It
       also prevents the cache from filling up with clients that  passed  some
       deep protocol test once and never came back.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_command_count_limit (default: 20)
       The  limit  on  the  total  number  of  commands	 per  SMTP session for
       postscreen(8)'s built-in SMTP protocol engine.  This SMTP engine defers
       or  rejects all attempts to deliver mail, therefore there is no need to
       enforce separate limits on the number of junk commands and  error  com‐
       mands.

       This feature is available in Postfix 2.8.

postscreen_command_time_limit (default: ${stress?10}${stress:300}s)
       The  command "read" time limit for postscreen(8)'s built-in SMTP proto‐
       col engine.

       This feature is available in Postfix 2.8.

postscreen_disable_vrfy_command (default: $disable_vrfy_command)
       Disable the SMTP VRFY command in the postscreen(8)  daemon.   See  dis‐
       able_vrfy_command for details.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_action (default: ignore)
       The  action  that  postscreen(8)	 takes	when an SMTP client's combined
       DNSBL score is equal to or greater than a threshold  (as	 defined  with
       the  postscreen_dnsbl_sites and postscreen_dnsbl_threshold parameters).
       Specify one of the following:

       ignore (default)
	      Ignore the failure of this test. Allow other tests to  complete.
	      Repeat this test the next time the client connects.  This option
	      is useful for testing and collecting statistics without blocking
	      mail.

       enforce
	      Allow  other  tests to complete. Reject attempts to deliver mail
	      with a 550 SMTP reply, and log the helo/sender/recipient	infor‐
	      mation.  Repeat this test the next time the client connects.

       drop   Drop  the	 connection  immediately with a 521 SMTP reply. Repeat
	      this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_reply_map (default: empty)
       A mapping from actual DNSBL domain name which includes a	 secret	 pass‐
       word,  to the DNSBL domain name that postscreen will reply with when it
       rejects mail.  When no mapping is found, the actual DNSBL  domain  will
       be used.

       For maximal stability it is best to use a file that is read into memory
       such as pcre:, regexp: or texthash: (texthash:  is  similar  to	hash:,
       except  a)  there  is  no need to run postmap(1) before the file can be
       used, and b) texthash: does not detect changes after the file is read).

       Example:

       /usr/local/etc/postfix/main.cf:
	   postscreen_dnsbl_reply_map = texthash:$config_directory/dnsbl_reply

       /usr/local/etc/postfix/dnsbl_reply:
	  secret.zen.spamhaus.org    zen.spamhaus.org

       This feature is available in Postfix 2.8.

postscreen_dnsbl_sites (default: empty)
       Optional list of DNS blocklist domains,	filters	 and  weight  factors.
       When  the  list	is  non-empty,	the dnsblog(8) daemon will query these
       domains with the IP addresses of non-whitelisted remote	SMTP  clients,
       and  postscreen(8)  will	 update an SMTP client's DNSBL score with each
       non-error reply.

       Caution: when postscreen rejects mail, it replies with the DNSBL domain
       name.  Use  the	postscreen_dnsbl_reply_map  feature to hide "password"
       information in DNSBL domain names.

       When a client's score is equal to or greater than the threshold	speci‐
       fied  with  postscreen_dnsbl_threshold, postscreen(8) can drop the con‐
       nection with the SMTP client.

       Specify a list of domain=filter*weight entries, separated by  comma  or
       whitespace.

       ·      When  no "=filter" is specified, postscreen(8) will use any non-
	      error DNSBL reply.   Otherwise,  the  filter  must  be  an  IPv4
	      address,	and  postscreen(8)  uses only DNSBL replies that match
	      the filter.

       ·      When no "*weight" is  specified,	postscreen(8)  increments  the
	      SMTP  client's  DNSBL score by 1.	 Otherwise, the weight must be
	      an integral number, and postscreen(8) adds the specified	weight
	      to the SMTP client's DNSBL score.	 Specify a negative number for
	      whitelisting.

       ·      When one postscreen_dnsbl_sites entry  produces  multiple	 DNSBL
	      responses, postscreen(8) applies the weight at most once.

       Examples:

       To  use	example.com  as a high-confidence blocklist, and to block mail
       with example.net and example.org only when both agree:

       postscreen_dnsbl_threshold = 2
       postscreen_dnsbl_sites = example.com*2, example.net, example.org

       To filter only DNSBL replies containing 127.0.0.4:

       postscreen_dnsbl_sites = example.com=127.0.0.4

       This feature is available in Postfix 2.8.

postscreen_dnsbl_threshold (default: 1)
       The inclusive lower bound for blocking an SMTP  client,	based  on  its
       combined DNSBL score as defined with the postscreen_dnsbl_sites parame‐
       ter.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_ttl (default: 1h)
       The amount of time that postscreen(8) will cache results	 from  a  suc‐
       cessful	DNS blocklist test. During this time, the client IP address is
       excluded from this test. The default is	relatively  short,  because  a
       good client can immediately talk to a real Postfix SMTP server.

       Specify	a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).  Time units: s  (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_forbidden_commands (default: $smtpd_forbidden_commands)
       List  of	 commands that the postscreen(8) server considers in violation
       of the SMTP protocol.  See  smtpd_forbidden_commands  for  syntax,  and
       postscreen_non_smtp_command_action for possible actions.

       This feature is available in Postfix 2.8.

postscreen_greet_action (default: ignore)
       The  action  that postscreen(8) takes when an SMTP client speaks before
       its turn within	the  time  specified  with  the	 postscreen_greet_wait
       parameter.  Specify one of the following:

       ignore (default)
	      Ignore  the failure of this test. Allow other tests to complete.
	      Repeat this test the next time the client connects.  This option
	      is useful for testing and collecting statistics without blocking
	      mail.

       enforce
	      Allow other tests to complete. Reject attempts to	 deliver  mail
	      with  a 550 SMTP reply, and log the helo/sender/recipient infor‐
	      mation.  Repeat this test the next time the client connects.

       drop   Drop the connection immediately with a 521  SMTP	reply.	Repeat
	      this test the next time the client connects.

       In  either  case,  postscreen(8)	 will not whitelist the SMTP client IP
       address.

       This feature is available in Postfix 2.8.

postscreen_greet_banner (default: $smtpd_banner)
       The  text  in  the  optional   "220-text..."   server   response	  that
       postscreen(8)  sends  ahead  of	the  real  Postfix  SMTP server's "220
       text..." response, in an attempt to confuse bad SMTP  clients  so  that
       they  speak  before  their turn (pre-greet).  Specify an empty value to
       disable this feature.

       This feature is available in Postfix 2.8.

postscreen_greet_ttl (default: 1d)
       The amount of time that postscreen(8) will cache results	 from  a  suc‐
       cessful	PREGREET  test.	 During	 this  time,  the client IP address is
       excluded from this test. The default is	relatively  short,  because  a
       good client can immediately talk to a real Postfix SMTP server.

       Specify	a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).  Time units: s  (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_greet_wait (default: ${stress?2}${stress:6}s)
       The  amount  of time that postscreen(8) will wait for an SMTP client to
       send a command before its turn, and for DNS blocklist lookup results to
       arrive  (default:  up to 2 seconds under stress, up to 6 seconds other‐
       wise).

       Specify a non-zero time value (an integral value plus an optional  one-
       letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_helo_required (default: $smtpd_helo_required)
       Require	that a remote SMTP client sends HELO or EHLO before commencing
       a MAIL transaction.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_action (default: drop)
       The action that postscreen(8) takes when an SMTP client sends  non-SMTP
       commands as specified with the postscreen_forbidden_commands parameter.
       Specify one of the following:

       ignore Ignore the failure of this test. Allow other tests to  complete.
	      Do  not  repeat this test before some the result from some other
	      test expires.  This option is useful for testing and  collecting
	      statistics without blocking mail permanently.

       enforce
	      Allow  other  tests to complete. Reject attempts to deliver mail
	      with a 550 SMTP reply, and log the helo/sender/recipient	infor‐
	      mation.  Repeat this test the next time the client connects.

       drop   Drop  the	 connection  immediately with a 521 SMTP reply. Repeat
	      this test the next time the client connects. This action is  the
	      same  as with the Postfix SMTP server's smtpd_forbidden_commands
	      feature.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_enable (default: no)
       Enable "non-SMTP command" tests	in  the	 postscreen(8)	server.	 These
       tests are expensive: a client must disconnect after it passes the test,
       before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_ttl (default: 30d)
       The amount of time that postscreen(8) will cache results	 from  a  suc‐
       cessful	"non_smtp_command"  SMTP  protocol test. During this time, the
       client IP address is excluded from  this	 test.	The  default  is  long
       because	a  client  must disconnect after it passes the test, before it
       can talk to a real Postfix SMTP server.

       Specify a non-zero time value (an integral value plus an optional  one-
       letter  suffix that specifies the time unit).  Time units: s (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_pipelining_action (default: enforce)
       The action that postscreen(8) takes when an SMTP client sends  multiple
       commands	 instead  of sending one command and waiting for the server to
       respond.	 Specify one of the following:

       ignore Ignore the failure of this test. Allow other tests to  complete.
	      Do  not  repeat this test before some the result from some other
	      test expires.  This option is useful for testing and  collecting
	      statistics without blocking mail permanently.

       enforce
	      Allow  other  tests to complete. Reject attempts to deliver mail
	      with a 550 SMTP reply, and log the helo/sender/recipient	infor‐
	      mation.  Repeat this test the next time the client connects.

       drop   Drop  the	 connection  immediately with a 521 SMTP reply. Repeat
	      this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_pipelining_enable (default: no)
       Enable "pipelining" SMTP protocol tests in  the	postscreen(8)  server.
       These  tests  are  expensive:  a	 good  client must disconnect after it
       passes the test, before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_pipelining_ttl (default: 30d)
       The amount of time that postscreen(8) will cache results	 from  a  suc‐
       cessful	"pipelining"  SMTP protocol test. During this time, the client
       IP address is excluded from this test. The default is  long  because  a
       good  client  must  disconnect  after it passes the test, before it can
       talk to a real Postfix SMTP server.

       Specify a non-zero time value (an integral value plus an optional  one-
       letter  suffix that specifies the time unit).  Time units: s (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_post_queue_limit (default: $default_process_limit)
       The number of clients that can be waiting for service from a real  SMTP
       server process. When this queue is full, all clients will receive a 421
       reponse.

       This feature is available in Postfix 2.8.

postscreen_pre_queue_limit (default: $default_process_limit)
       The number of non-whitelisted clients that can be waiting for  a	 deci‐
       sion whether they will receive service from a real SMTP server process.
       When this queue is full, all non-whitelisted clients will receive a 421
       reponse.

       This feature is available in Postfix 2.8.

postscreen_watchdog_timeout (default: 10s)
       How  much  time	a postscreen(8) process may take to respond to an SMTP
       client command or to perform a cache operation before it is  terminated
       by a built-in watchdog timer.  This is a safety mechanism that prevents
       postscreen(8) from becoming non-responsive due  to  a  bug  in  Postfix
       itself  or  in  system software.	 To avoid false alarms and unnecessary
       cache corruption this limit cannot be set under 10s.

       Specify a non-zero time value (an integral value plus an optional  one-
       letter  suffix that specifies the time unit).  Time units: s (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_whitelist_networks (default: $mynetworks)
       Network addresses that are permanently whitelisted, and that  will  not
       be  subjected  to  postscreen(8)	 checks.  This parameter uses the same
       address syntax as the mynetworks parameter. This feature never uses the
       remote SMTP client hostname.

       This feature is available in Postfix 2.8.

prepend_delivered_header (default: command, file, forward)
       The message delivery contexts where the Postfix local(8) delivery agent
       prepends a Delivered-To:	 message header with the address that the mail
       was  delivered  to.  This  information  is  used for mail delivery loop
       detection.

       By default, the Postfix local delivery agent prepends  a	 Delivered-To:
       header  when  forwarding mail and when delivering to file (mailbox) and
       command. Turning off the Delivered-To: header when forwarding  mail  is
       not recommended.

       Specify zero or more of forward, file, or command.

       Example:

       prepend_delivered_header = forward

process_id (read-only)
       The process ID of a Postfix command or daemon process.

process_id_directory (default: pid)
       The  location  of Postfix PID files relative to $queue_directory.  This
       is a read-only parameter.

process_name (read-only)
       The process name of a Postfix command or daemon process.

propagate_unmatched_extensions (default: canonical, virtual)
       What address lookup tables copy an address extension  from  the	lookup
       key to the lookup result.

       For   example,	with  a	 virtual(5)  mapping  of  "joe@example.com  =>
       joe.user@example.net", the address "joe+foo@example.com" would  rewrite
       to "joe.user+foo@example.net".

       Specify	zero or more of canonical, virtual, alias, forward, include or
       generic. These cause address extension propagation  with	 canonical(5),
       virtual(5),  and	 aliases(5) maps, with local(8) .forward and :include:
       file lookups, and with smtp(8) generic maps, respectively.

       Note: enabling this feature for types other than canonical and  virtual
       is  likely  to  cause  problems	when mail is forwarded to other sites,
       especially with mail that is sent to a mailing list exploder address.

       Examples:

       propagate_unmatched_extensions = canonical, virtual, alias,
	       forward, include
       propagate_unmatched_extensions = canonical, virtual

proxy_interfaces (default: empty)
       The network interface addresses that this mail system receives mail  on
       by way of a proxy or network address translation unit.

       This feature is available in Postfix 2.0 and later.

       You must specify your "outside" proxy/NAT addresses when your system is
       a backup MX host for other domains, otherwise mail delivery loops  will
       happen when the primary MX host is down.

       Example:

       proxy_interfaces = 1.2.3.4

proxy_read_maps (default: see postconf -d output)
       The  lookup tables that the proxymap(8) server is allowed to access for
       the read-only service.  Table references that don't begin  with	proxy:
       are ignored.

       This feature is available in Postfix 2.0 and later.

proxy_write_maps (default: see postconf -d output)
       The  lookup tables that the proxymap(8) server is allowed to access for
       the read-write service. Postfix-owned local database  files  should  be
       stored  under  the Postfix-owned data_directory.	 Table references that
       don't begin with proxy: are ignored.

       This feature is available in Postfix 2.5 and later.

proxymap_service_name (default: proxymap)
       The name of the proxymap read-only table lookup service.	 This  service
       is normally implemented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

proxywrite_service_name (default: proxywrite)
       The  name of the proxywrite read-write table lookup service.  This ser‐
       vice is normally implemented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

qmgr_clog_warn_time (default: 300s)
       The minimal delay between warnings that a specific destination is clog‐
       ging up the Postfix active queue. Specify 0 to disable.

       This feature is enabled with the helpful_warnings parameter.

       This feature is available in Postfix 2.0 and later.

qmgr_daemon_timeout (default: 1000s)
       How  much  time	a  Postfix  queue manager process may take to handle a
       request before it is terminated by a built-in watchdog timer.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

qmgr_fudge_factor (default: 100)
       Obsolete feature: the percentage of delivery resources that a busy mail
       system will use up for delivery of a large mailing  list message.

       This feature exists only in the oqmgr(8) old queue manager. The current
       queue manager solves the problem in a better way.

qmgr_ipc_timeout (default: 60s)
       The  time  limit	 for  the queue manager to send or receive information
       over an internal communication channel.	The purpose is to break out of
       deadlock	 situations. If the time limit is exceeded the software either
       retries or aborts the operation.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

qmgr_message_active_limit (default: 20000)
       The maximal number of messages in the active queue.

qmgr_message_recipient_limit (default: 20000)
       The  maximal  number  of recipients held in memory by the Postfix queue
       manager, and the maximal size of the size of the short-term,  in-memory
       "dead" destination status cache.

qmgr_message_recipient_minimum (default: 10)
       The  minimal number of in-memory recipients for any message. This takes
       priority over any other in-memory recipient limits  (i.e.,  the	global
       qmgr_message_recipient_limit and the per transport _recipient_limit) if
       necessary. The minimum value allowed for this parameter is 1.

qmqpd_authorized_clients (default: empty)
       What clients are allowed to connect to the QMQP server port.

       By default, no client is allowed to use the service.  This  is  because
       the QMQP server will relay mail to any destination.

       Specify	a  list	 of  client  patterns. A list pattern specifies a host
       name, a domain name, an internet address, or  a	network/mask  pattern,
       where  the mask specifies the number of bits in the network part.  When
       a pattern specifies a file name, its contents are substituted  for  the
       file  name; when a pattern is a "type:table" table specification, table
       lookup is used instead.

       Patterns are separated by whitespace and/or commas. In order to reverse
       the  result,  precede a pattern with an exclamation point (!). The form
       "!/file/name" is supported only in Postfix version 2.4 and later.

       Example:

       qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24

qmqpd_client_port_logging (default: no)
       Enable logging of the remote QMQP client port in addition to the	 host‐
       name and IP address. The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

qmqpd_error_delay (default: 1s)
       How  long the QMQP server will pause before sending a negative reply to
       the client. The purpose is to slow down confused or malicious clients.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

qmqpd_timeout (default: 300s)
       The  time  limit for sending or receiving information over the network.
       If a read or write operation blocks for more than  $qmqpd_timeout  sec‐
       onds the QMQP server gives up and disconnects.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

queue_directory (default: see postconf -d output)
       The location of the Postfix top-level queue directory. This is the root
       directory of Postfix daemon processes that run chrooted.

queue_file_attribute_count_limit (default: 100)
       The  maximal  number of (name=value) attributes that may be stored in a
       Postfix queue file. The limit is enforced by the cleanup(8) server.

       This feature is available in Postfix 2.0 and later.

queue_minfree (default: 0)
       The minimal amount of free space in bytes in the queue file system that
       is  needed  to receive mail.  This is currently used by the SMTP server
       to decide if it will accept any mail at all.

       By default, the Postfix SMTP server rejects MAIL FROM commands when the
       amount of free space is less than 1.5*$message_size_limit (Postfix ver‐
       sion 2.1 and later).  To specify a higher  minimum  free	 space	limit,
       specify a queue_minfree value that is at least 1.5*$message_size_limit.

       With  Postfix  versions	2.0 and earlier, a queue_minfree value of zero
       means there is no minimum required amount of free space.

queue_run_delay (default: 300s)
       The time between deferred queue scans by the queue  manager;  prior  to
       Postfix 2.4 the default value was 1000s.

       This  parameter	should	be  set	 less  than or equal to $minimal_back‐
       off_time. See also $maximal_backoff_time.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

queue_service_name (default: qmgr)
       The name of the qmgr(8) service. This service manages the Postfix queue
       and schedules delivery requests.

       This feature is available in Postfix 2.0 and later.

rbl_reply_maps (default: empty)
       Optional lookup tables with RBL	response  templates.  The  tables  are
       indexed	by  the	 RBL domain name. By default, Postfix uses the default
       template as specified with the default_rbl_reply configuration  parame‐
       ter. See there for a discussion of the syntax of RBL reply templates.

       This feature is available in Postfix 2.0 and later.

readme_directory (default: see postconf -d output)
       The  location  of Postfix README files that describe how to build, con‐
       figure or operate a specific Postfix subsystem or feature.

receive_override_options (default: empty)
       Enable or disable recipient validation, built-in content filtering,  or
       address	mapping.  Typically,  these are specified in master.cf as com‐
       mand-line arguments for the smtpd(8), qmqpd(8) or pickup(8) daemons.

       Specify zero or more of the following options.	The  options  override
       main.cf	settings  and are either implemented by smtpd(8), qmqpd(8), or
       pickup(8) themselves, or they are forwarded to the cleanup server.

       no_unknown_recipient_checks
	      Do not try to reject  unknown  recipients	 (SMTP	server	only).
	      This is typically specified AFTER an external content filter.

       no_address_mappings
	      Disable  canonical address mapping, virtual alias map expansion,
	      address masquerading,  and  automatic  BCC  (blind  carbon-copy)
	      recipients.  This is typically specified BEFORE an external con‐
	      tent filter.

       no_header_body_checks
	      Disable header/body_checks. This is typically specified AFTER an
	      external content filter.

       no_milters
	      Disable  Milter  (mail  filter)  applications. This is typically
	      specified AFTER an external content filter.

       Note: when the "BEFORE content filter" receive_override_options setting
       is  specified  in  the main.cf file, specify the "AFTER content filter"
       receive_override_options setting in master.cf (and vice versa).

       Examples:

       receive_override_options =
	   no_unknown_recipient_checks, no_header_body_checks
       receive_override_options = no_address_mappings

       This feature is available in Postfix 2.1 and later.

recipient_bcc_maps (default: empty)
       Optional BCC (blind carbon-copy)	 address  lookup  tables,  indexed  by
       recipient  address.   The  BCC  address	(multiple results are not sup‐
       ported) is added when mail enters from outside of Postfix.

       This feature is available in Postfix 2.1 and later.

       The table search order is as follows:

       ·      Look up the "user+extension@domain.tld"  address	including  the
	      optional address extension.

       ·      Look  up	the  "user@domain.tld"	address	 without  the optional
	      address extension.

       ·      Look up the "user+extension" address local part when the recipi‐
	      ent domain equals $myorigin, $mydestination, $inet_interfaces or
	      $proxy_interfaces.

       ·      Look up the "user" address local part when the recipient	domain
	      equals	$myorigin,    $mydestination,	 $inet_interfaces   or
	      $proxy_interfaces.

       ·      Look up the "@domain.tld" part.

       Specify the types and names of databases to  use.   After  change,  run
       "postmap /usr/local/etc/postfix/recipient_bcc".

       Note:  if  mail	to  the BCC address bounces it will be returned to the
       sender.

       Note: automatic BCC recipients are produced  only  for  new  mail.   To
       avoid  mailer  loops,  automatic BCC recipients are not generated after
       Postfix forwards mail  internally,  or  after  Postfix  generates  mail
       itself.

       Example:

       recipient_bcc_maps = hash:$config_directory/recipient_bcc

recipient_canonical_classes (default: envelope_recipient, header_recipient)
       What addresses are subject to recipient_canonical_maps address mapping.
       By default, recipient_canonical_maps  address  mapping  is  applied  to
       envelope recipient addresses, and to header recipient addresses.

       Specify one or more of: envelope_recipient, header_recipient

       This feature is available in Postfix 2.2 and later.

recipient_canonical_maps (default: empty)
       Optional	 address mapping lookup tables for envelope and header recipi‐
       ent addresses.  The table format and lookups are documented in  canoni‐
       cal(5).

       Note: $recipient_canonical_maps is processed before $canonical_maps.

       Example:

       recipient_canonical_maps = hash:$config_directory/recipient_canonical

recipient_delimiter (default: empty)
       The  separator  between	user  names and address extensions (user+foo).
       See canonical(5), local(8), relocated(5) and virtual(5) for the effects
       this has on aliases, canonical, virtual, relocated and on .forward file
       lookups.	 Basically,  the  software  tries  user+foo  and  .forward+foo
       before trying user and .forward.

       Example:

       recipient_delimiter = +

reject_code (default: 554)
       The  numerical  Postfix	SMTP  server  response code when a remote SMTP
       client request is rejected by the "reject" restriction.

       Do not change this unless you have  a  complete	understanding  of  RFC
       2821.

reject_tempfail_action (default: defer_if_permit)
       The  Postfix  SMTP server's action when a reject-type restriction fails
       due to a temporary error condition. Specify "defer" to defer the remote
       SMTP  client  request  immediately.  With the default "defer_if_permit"
       action, the Postfix SMTP server continues to look for opportunities  to
       reject  mail,  and defers the client request only if it would otherwise
       be accepted.

       For finer control, see:	unverified_recipient_tempfail_action,  unveri‐
       fied_sender_tempfail_action,    unknown_address_tempfail_action,	   and
       unknown_helo_hostname_tempfail_action.

       This feature is available in Postfix 2.6 and later.

relay_clientcerts (default: empty)
       List of tables with remote  SMTP	 client-certificate  fingerprints  for
       which  the  Postfix  SMTP  server  will	allow  access  with  the  per‐
       mit_tls_clientcerts feature.  The fingerprint digest algorithm is  con‐
       figurable via the smtpd_tls_fingerprint_digest parameter (hard-coded as
       md5 prior to Postfix version 2.5).

       Postfix lookup tables are in the form of (key, value) pairs.  Since  we
       only  need  the	key, the value can be chosen freely, e.g.  the name of
       the  user  or   host:   D7:04:2F:A7:0B:8C:A5:21:FA:31:77:E1:41:8A:EE:80
       lutzpc.at.home

       Example:

       relay_clientcerts = hash:$config_directory/relay_clientcerts

       For  more  fine-grained	control,  use  check_ccert_access to select an
       appropriate  access(5)  policy	for   each   client.	See   RESTRIC‐
       TION_CLASS_README.

       This feature is available with Postfix version 2.2.

relay_destination_concurrency_limit   (default:	  $default_destination_concur‐
       rency_limit)
       The maximal number of parallel deliveries to the same  destination  via
       the  relay  message  delivery  transport. This limit is enforced by the
       queue manager. The message delivery transport name is the  first	 field
       in the entry in the master.cf file.

       This feature is available in Postfix 2.0 and later.

relay_destination_recipient_limit    (default:	  $default_destination_recipi‐
       ent_limit)
       The maximal number of recipients per  message  for  the	relay  message
       delivery	 transport.  This  limit is enforced by the queue manager. The
       message delivery transport name is the first field in the entry in  the
       master.cf file.

       Setting	this  parameter	 to  a	value  of  1  changes  the  meaning of
       relay_destination_concurrency_limit from concurrency  per  domain  into
       concurrency per recipient.

       This feature is available in Postfix 2.0 and later.

relay_domains (default: $mydestination)
       What  destination  domains  (and	 subdomains  thereof) this system will
       relay  mail  to.	 Subdomain  matching  is  controlled  with  the	  par‐
       ent_domain_matches_subdomains  parameter.  For  details	about  how the
       relay_domains  value  is	 used,	see  the  description  of   the	  per‐
       mit_auth_destination   and   reject_unauth_destination  SMTP  recipient
       restrictions.

       Domains that match $relay_domains are delivered with the	 $relay_trans‐
       port  mail  delivery  transport.	 The  SMTP  server validates recipient
       addresses with $relay_recipient_maps and rejects	 non-existent  recipi‐
       ents.   See   also   the	  relay	  domains   address   class   in   the
       ADDRESS_CLASS_README file.

       Note: Postfix will not automatically forward mail for domains that list
       this  system  as	 their	primary	 or  backup  MX	 host.	See  the  per‐
       mit_mx_backup restriction in the postconf(5) manual page.

       Specify a list of  host	or  domain  names,  "/file/name"  patterns  or
       "type:table"  lookup  tables,  separated	 by  commas and/or whitespace.
       Continue long lines by  starting	 the  next  line  with	whitespace.  A
       "/file/name" pattern is replaced by its contents; a "type:table" lookup
       table is matched when a (parent) domain appears as lookup key.  Specify
       "!pattern" to exclude a domain from the list. The form "!/file/name" is
       supported only in Postfix version 2.4 and later.

relay_domains_reject_code (default: 554)
       The numerical Postfix SMTP server response code when a  client  request
       is rejected by the reject_unauth_destination recipient restriction.

       Do  not	change	this  unless  you have a complete understanding of RFC
       2821.

relay_recipient_maps (default: empty)
       Optional lookup tables with all valid addresses	in  the	 domains  that
       match  $relay_domains.  Specify @domain as a wild-card for domains that
       have no valid recipient list, and become a source of backscatter	 mail:
       Postfix	accepts spam for non-existent recipients and then floods inno‐
       cent people with undeliverable mail.  Technically, tables  listed  with
       $relay_recipient_maps  are used as lists: Postfix needs to know only if
       a lookup string is found or not, but it does not use  the  result  from
       table lookup.

       If  this	 parameter  is	non-empty,  then  the Postfix SMTP server will
       reject mail to unknown relay users. This feature is off by default.

       See also the relay domains address class	 in  the  ADDRESS_CLASS_README
       file.

       Example:

       relay_recipient_maps = hash:$config_directory/relay_recipients

       This feature is available in Postfix 2.0 and later.

relay_transport (default: relay)
       The default mail delivery transport and next-hop destination for remote
       delivery to domains listed with $relay_domains. In order of  decreasing
       precedence,  the	 nexthop  destination  is taken from $relay_transport,
       $sender_dependent_relayhost_maps, $relayhost,  or  from	the  recipient
       domain. This information can be overruled with the transport(5) table.

       Specify	a string of the form transport:nexthop, where transport is the
       name of a mail delivery transport defined in master.cf.	 The  :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       See also the relay domains address class	 in  the  ADDRESS_CLASS_README
       file.

       This feature is available in Postfix 2.0 and later.

relayhost (default: empty)
       The next-hop destination of non-local mail; overrides non-local domains
       in recipient addresses. This information is overruled with relay_trans‐
       port,	sender_dependent_default_transport_maps,    default_transport,
       sender_dependent_relayhost_maps and with the transport(5) table.

       On an intranet, specify the organizational domain name. If your	inter‐
       nal  DNS	 uses  no MX records, specify the name of the intranet gateway
       host instead.

       In the case of SMTP, specify a domain  name,  hostname,	hostname:port,
       [hostname]:port,	 [hostaddress]	or [hostaddress]:port. The form [host‐
       name] turns off MX lookups.

       If you're connected via UUCP,  see  the	UUCP_README  file  for	useful
       information.

       Examples:

       relayhost = $mydomain
       relayhost = [gateway.example.com]
       relayhost = uucphost
       relayhost = [an.ip.add.ress]

relocated_maps (default: empty)
       Optional	 lookup	 tables	 with  new  contact  information  for users or
       domains that no longer exist.  The table format and lookups  are	 docu‐
       mented in relocated(5).

       If you use this feature, run "postmap /usr/local/etc/postfix/relocated"
       to build the necessary DBM or  DB  file	after  change,	then  "postfix
       reload" to make the changes visible.

       Examples:

       relocated_maps = dbm:$config_directory/relocated
       relocated_maps = hash:$config_directory/relocated

remote_header_rewrite_domain (default: empty)
       Don't  rewrite  message	headers	 from  remote clients at all when this
       parameter is empty; otherwise, rewrite message headers and  append  the
       specified  domain  name	to incomplete addresses.  The local_header_re‐
       write_clients parameter controls what clients Postfix considers local.

       Examples:

       The  safe  setting:  append  "domain.invalid"  to   incomplete	header
       addresses  from	remote SMTP clients, so that those addresses cannot be
       confused with local addresses.

	   remote_header_rewrite_domain = domain.invalid

       The default, purist, setting: don't rewrite headers from remote clients
       at all.

	   remote_header_rewrite_domain =

require_home_directory (default: no)
       Require	that  a local(8) recipient's home directory exists before mail
       delivery is attempted. By default this test is  disabled.   It  can  be
       useful for environments that import home directories to the mail server
       (IMPORTING HOME DIRECTORIES IS NOT RECOMMENDED).

reset_owner_alias (default: no)
       Reset the local(8) delivery agent's idea of the owner-alias  attribute,
       when  delivering mail to a child alias that does not have its own owner
       alias.

       This feature is available in Postfix 2.8 and later. With older  Postfix
       releases, the behavior is as if this parameter is set to "yes".

       As  documented  in aliases(5), when an alias name has a companion alias
       named owner-name, delivery errors will be reported to the  owner	 alias
       instead	of  the	 sender. This configuration is recommended for mailing
       lists.

       A less known property of the owner alias is that	 it  also  forces  the
       local(8)	 delivery agent to write local and remote addresses from alias
       expansion to a new queue file, instead of attempting to deliver mail to
       local addresses as soon as they come out of alias expansion.

       Writing local addresses from alias expansion to a new queue file allows
       for robust handling of temporary delivery errors: errors with one local
       member  have  no effect on deliveries to other members of the list.  On
       the other hand, delivery to local addresses as soon as they come out of
       alias  expansion	 is  fragile: a temporary error with one local address
       from alias expansion will cause the entire alias to be expanded repeat‐
       edly  until  the	 error	goes away, or until the message expires in the
       queue.  In that case, a problem with one list member results in	multi‐
       ple message deliveries to other list members.

       The  default  behavior  of  Postfix 2.8 and later is to keep the owner-
       alias attribute of the parent alias, when delivering mail  to  a	 child
       alias  that  does  not  have its own owner alias. Then, local addresses
       from that child alias will be written to a new queue file, and a tempo‐
       rary  error  with  one  local address will not affect delivery to other
       mailing list members.

       Unfortunately, older Postfix releases reset the	owner-alias  attribute
       when  delivering mail to a child alias that does not have its own owner
       alias.  The local(8) delivery agent  then  attempts  to	deliver	 local
       addresses as soon as they come out of child alias expansion.  If deliv‐
       ery to any address from child alias expansion fails  with  a  temporary
       error  condition,  the  entire  mailing list may be expanded repeatedly
       until the mail expires in the queue, resulting in  multiple  deliveries
       of the same message to mailing list members.

resolve_dequoted_address (default: yes)
       Resolve	a  recipient  address  safely instead of correctly, by looking
       inside quotes.

       By default, the Postfix address resolver does  not  quote  the  address
       localpart  as  per  RFC	822, so that additional @ or % or !  operators
       remain visible. This behavior is safe but it is also technically incor‐
       rect.

       If  you	specify	 "resolve_dequoted_address  =  no",  then  the Postfix
       resolver will not know about additional @ etc. operators in the address
       localpart. This opens opportunities for obscure mail relay attacks with
       user@domain@domain addresses when Postfix provides  backup  MX  service
       for Sendmail systems.

resolve_null_domain (default: no)
       Resolve	an  address  that  ends in the "@" null domain as if the local
       hostname were specified, instead of rejecting the address as invalid.

       This feature is available in Postfix 2.1 and later.   Earlier  versions
       always resolve the null domain as the local hostname.

       The  Postfix  SMTP  server  uses this feature to reject mail from or to
       addresses that end in the "@" null domain, and from addresses that  re‐
       write into a form that ends in the "@" null domain.

resolve_numeric_domain (default: no)
       Resolve	"user@ipaddress"  as  "user@[ipaddress]", instead of rejecting
       the address as invalid.

       This feature is available in Postfix 2.3 and later.

rewrite_service_name (default: rewrite)
       The name of  the	 address  rewriting  service.  This  service  rewrites
       addresses  to  standard	form  and resolves them to a (delivery method,
       next-hop host, recipient) triple.

       This feature is available in Postfix 2.0 and later.

sample_directory (default: /usr/local/etc/postfix)
       The name of the directory with  example	Postfix	 configuration	files.
       Starting	 with  Postfix	2.1,  these  files have been replaced with the
       postconf(5) manual page.

send_cyrus_sasl_authzid (default: no)
       When authenticating to a remote SMTP or LMTP server  with  the  default
       setting	"no",  send  no SASL authoriZation ID (authzid); send only the
       SASL authentiCation ID (authcid) plus the authcid's password.

       The non-default setting "yes" enables the  behavior  of	older  Postfix
       versions.   These  always send a SASL authzid that is equal to the SASL
       authcid, but this causes	 inter-operability  problems  with  some  SMTP
       servers.

       This feature is available in Postfix 2.4.4 and later.

sender_based_routing (default: no)
       This  parameter	should	not  be used. It was replaced by sender_depen‐
       dent_relayhost_maps in Postfix version 2.3.

sender_bcc_maps (default: empty)
       Optional BCC (blind carbon-copy)	 address  lookup  tables,  indexed  by
       sender  address.	  The BCC address (multiple results are not supported)
       is added when mail enters from outside of Postfix.

       This feature is available in Postfix 2.1 and later.

       The table search order is as follows:

       ·      Look up the "user+extension@domain.tld"  address	including  the
	      optional address extension.

       ·      Look  up	the  "user@domain.tld"	address	 without  the optional
	      address extension.

       ·      Look up the "user+extension" address local part when the	sender
	      domain  equals  $myorigin,  $mydestination,  $inet_interfaces or
	      $proxy_interfaces.

       ·      Look up the "user" address local part  when  the	sender	domain
	      equals	$myorigin,    $mydestination,	 $inet_interfaces   or
	      $proxy_interfaces.

       ·      Look up the "@domain.tld" part.

       Specify the types and names of databases to  use.   After  change,  run
       "postmap /usr/local/etc/postfix/sender_bcc".

       Note:  if  mail	to  the BCC address bounces it will be returned to the
       sender.

       Note: automatic BCC recipients are produced  only  for  new  mail.   To
       avoid  mailer  loops,  automatic BCC recipients are not generated after
       Postfix forwards mail  internally,  or  after  Postfix  generates  mail
       itself.

       Example:

       sender_bcc_maps = hash:$config_directory/sender_bcc

sender_canonical_classes (default: envelope_sender, header_sender)
       What  addresses	are  subject to sender_canonical_maps address mapping.
       By default, sender_canonical_maps address mapping is applied  to	 enve‐
       lope sender addresses, and to header sender addresses.

       Specify one or more of: envelope_sender, header_sender

       This feature is available in Postfix 2.2 and later.

sender_canonical_maps (default: empty)
       Optional	 address  mapping lookup tables for envelope and header sender
       addresses.  The table format and	 lookups  are  documented  in  canoni‐
       cal(5).

       Example:	 you  want to rewrite the SENDER address "user@ugly.domain" to
       "user@pretty.domain", while still being able to send mail to the RECIP‐
       IENT address "user@ugly.domain".

       Note: $sender_canonical_maps is processed before $canonical_maps.

       Example:

       sender_canonical_maps = hash:$config_directory/sender_canonical

sender_dependent_default_transport_maps (default: empty)
       A  sender-dependent override for the global default_transport parameter
       setting. The tables are searched by the	envelope  sender  address  and
       @domain.	 A  lookup result of DUNNO terminates the search without over‐
       riding the global default_transport parameter setting.	This  informa‐
       tion is overruled with the transport(5) table.

       Note:  this overrides default_transport, not transport_maps, and there‐
       fore the expected syntax is that of default_transport, not  the	syntax
       of  transport_maps.   Specifically,  this  does	not support the trans‐
       port_maps syntax for  null  transport,  null  nexthop,  or  null	 email
       addresses.

       For  safety  reasons, this feature does not allow $number substitutions
       in regular expression maps.

       This feature is available in Postfix 2.7 and later.

sender_dependent_relayhost_maps (default: empty)
       A sender-dependent override for the global relayhost parameter setting.
       The  tables  are searched by the envelope sender address and @domain. A
       lookup result of DUNNO terminates the  search  without  overriding  the
       global relayhost parameter setting (Postfix 2.6 and later). This infor‐
       mation	 is    overruled    with    relay_transport,	 sender_depen‐
       dent_default_transport_maps,  default_transport	and  with  the	trans‐
       port(5) table.

       For safety reasons, this feature does not allow	$number	 substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

sendmail_path (default: see postconf -d output)
       A  Sendmail  compatibility  feature  that specifies the location of the
       Postfix sendmail(1) command. This command can be used  to  submit  mail
       into the Postfix queue.

service_throttle_time (default: 60s)
       How  long  the  Postfix	master(8)  waits  before forking a server that
       appears to be malfunctioning.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

setgid_group (default: postdrop)
       The  group  ownership of set-gid Postfix commands and of group-writable
       Postfix directories. When this parameter value is changed you  need  to
       re-run "postfix set-permissions" (with Postfix version 2.0 and earlier:
       "/usr/local/etc/postfix/post-install set-permissions".

show_user_unknown_table_name (default: yes)
       Display	the  name  of  the  recipient  table  in  the  "User  unknown"
       responses.   The	 extra	detail	makes trouble shooting easier but also
       reveals information that is nobody elses business.

       This feature is available in Postfix 2.0 and later.

showq_service_name (default: showq)
       The name of the showq(8) service. This service produces mail queue sta‐
       tus reports.

       This feature is available in Postfix 2.0 and later.

smtp_address_preference (default: ipv6)
       The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP client
       will try first, when a destination has IPv6  and	 IPv4  addresses  with
       equal  MX preference. This feature has no effect unless the inet_proto‐
       cols setting enables both IPv4 and IPv6.

       This feature is available in Postfix 2.8 and later.

smtp_always_send_ehlo (default: yes)
       Always send EHLO at the start of an SMTP session.

       With "smtp_always_send_ehlo = no", Postfix sends	 EHLO  only  when  the
       word  "ESMTP"  appears  in  the	server	greeting  banner (example: 220
       spike.porcupine.org ESMTP Postfix).

smtp_bind_address (default: empty)
       An optional numerical network address  that  the	 Postfix  SMTP	client
       should bind to when making an IPv4 connection.

       This  can  be specified in the main.cf file for all SMTP clients, or it
       can be specified in the master.cf file for a specific client, for exam‐
       ple:

	   /usr/local/etc/postfix/master.cf:
	       smtp ... smtp -o smtp_bind_address=11.22.33.44

       Note  1:	 when inet_interfaces specifies no more than one IPv4 address,
       and that address is a non-loopback address, it is automatically used as
       the  smtp_bind_address.	This supports virtual IP hosting, but can be a
       problem on multi-homed firewalls. See the inet_interfaces documentation
       for more detail.

       Note 2: address information may be enclosed inside [], but this form is
       not required here.

smtp_bind_address6 (default: empty)
       An optional numerical network address  that  the	 Postfix  SMTP	client
       should bind to when making an IPv6 connection.

       This feature is available in Postfix 2.2 and later.

       This  can  be specified in the main.cf file for all SMTP clients, or it
       can be specified in the master.cf file for a specific client, for exam‐
       ple:

	   /usr/local/etc/postfix/master.cf:
	       smtp ... smtp -o smtp_bind_address6=1:2:3:4:5:6:7:8

       Note  1:	 when inet_interfaces specifies no more than one IPv6 address,
       and that address is a non-loopback address, it is automatically used as
       the smtp_bind_address6.	This supports virtual IP hosting, but can be a
       problem on multi-homed firewalls. See the inet_interfaces documentation
       for more detail.

       Note 2: address information may be enclosed inside [], but this form is
       not recommended here.

smtp_body_checks (default: empty)
       Restricted body_checks(5) tables for the Postfix	 SMTP  client.	 These
       tables are searched while mail is being delivered.  Actions that change
       the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_cname_overrides_servername (default: version dependent)
       Allow DNS CNAME records to override the	servername  that  the  Postfix
       SMTP  client  uses  for logging, SASL password lookup, TLS policy deci‐
       sions, or TLS certificate verification. The value "no" hardens  Postfix
       smtp_tls_per_site hostname-based policies against false hostname infor‐
       mation in DNS CNAME records, and makes SASL password file lookups  more
       predictable. This is the default setting as of Postfix 2.3.

       This feature is available in Postfix 2.2.9 and later.

smtp_connect_timeout (default: 30s)
       The  SMTP  client  time	limit for completing a TCP connection, or zero
       (use the operating system built-in time limit).

       When no connection can be made within the deadline,  the	 Postfix  SMTP
       client  tries the next address on the mail exchanger list. Specify 0 to
       disable the time limit (i.e. use whatever timeout is implemented by the
       operating system).

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_connection_cache_destinations (default: empty)
       Permanently enable SMTP connection caching for the  specified  destina‐
       tions.	With SMTP connection caching, a connection is not closed imme‐
       diately after completion of a mail transaction.	Instead,  the  connec‐
       tion  is kept open for up to $smtp_connection_cache_time_limit seconds.
       This allows connections to be reused  for  other	 deliveries,  and  can
       improve mail delivery performance.

       Specify	a  comma  or  white  space  separated  list of destinations or
       pseudo-destinations:

       ·      if mail is sent without a relay host: a domain name (the	right-
	      hand  side  of an email address, without the [] around a numeric
	      IP address),

       ·      if mail is sent via a relay host: a relay host name (without  []
	      or  non-default  TCP  port),  as	specified in main.cf or in the
	      transport map,

       ·      if mail is sent via a UNIX-domain socket:	 a  pathname  (without
	      the unix: prefix),

       ·      a	 /file/name  with  domain  names  and/or  relay	 host names as
	      defined above,

       ·      a "type:table" with domain names and/or relay host names on  the
	      left-hand	 side.	 The  right-hand side result from "type:table"
	      lookups is ignored.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_on_demand (default: yes)
       Temporarily enable SMTP connection caching while a  destination	has  a
       high volume of mail in the active queue.	 With SMTP connection caching,
       a connection is not closed  immediately	after  completion  of  a  mail
       transaction.  Instead, the connection is kept open for up to $smtp_con‐
       nection_cache_time_limit seconds.  This allows connections to be reused
       for other deliveries, and can improve mail delivery performance.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_reuse_limit (default: 10)
       When  SMTP  connection  caching is enabled, the number of times that an
       SMTP session may be reused before it is closed.

       This feature is available in Postfix 2.2. In Postfix 2.3 it is replaced
       by $smtp_connection_reuse_time_limit.

smtp_connection_cache_time_limit (default: 2s)
       When  SMTP  connection  caching	is enabled, the amount of time that an
       unused SMTP client socket is kept open before it	 is  closed.   Do  not
       specify larger values without permission from the remote sites.

       This feature is available in Postfix 2.2 and later.

smtp_connection_reuse_time_limit (default: 300s)
       The  amount  of	time  during which Postfix will use an SMTP connection
       repeatedly.  The timer starts when the connection is initiated (i.e. it
       includes	 the  connect,	greeting  and helo latency, in addition to the
       latencies of subsequent mail delivery transactions).

       This feature addresses a performance stability problem with remote SMTP
       servers.	 This  problem	is not specific to Postfix: it can happen when
       any MTA sends large amounts of SMTP email to a site that	 has  multiple
       MX hosts.

       The  problem  starts  when one of a set of MX hosts becomes slower than
       the rest.  Even though SMTP clients connect to fast and slow  MX	 hosts
       with equal probability, the slow MX host ends up with more simultaneous
       inbound connections than the faster MX hosts, because the slow MX  host
       needs more time to serve each client request.

       The  slow  MX  host  becomes  a	connection  attractor.	If one MX host
       becomes N times slower  than  the  rest,	 it  dominates	mail  delivery
       latency	unless	there  are  more  than	N fast MX hosts to counter the
       effect. And if the number of MX hosts  is  smaller  than	 N,  the  mail
       delivery	 latency  becomes  effectively	that  of  the  slowest MX host
       divided by the total number of MX hosts.

       The solution uses connection caching in a way that differs from Postfix
       version	2.2.  By limiting the amount of time during which a connection
       can be used repeatedly (instead of limiting the	number	of  deliveries
       over  that  connection), Postfix not only restores fairness in the dis‐
       tribution of simultaneous connections across a set of MX hosts, it also
       favors  deliveries over connections that perform well, which is exactly
       what we want.

       The default reuse time limit, 300s, is comparable to the	 various  smtp
       transaction timeouts which are fair estimates of maximum excess latency
       for a slow delivery.  Note that hosts may accept thousands of  messages
       over  a	single	connection  within  the	 default connection reuse time
       limit. This number is much larger than the default Postfix version  2.2
       limit  of  10 messages per cached connection. It may prove necessary to
       lower the limit to avoid interoperability issues with MTAs that exhibit
       bugs when many messages are delivered via a single connection.  A lower
       reuse time limit risks losing the benefit of connection reuse when  the
       average	connection  and	 mail  delivery latency exceeds the reuse time
       limit.

       This feature is available in Postfix 2.3 and later.

smtp_data_done_timeout (default: 600s)
       The SMTP client time limit for sending the SMTP ".", and for  receiving
       the server response.

       When  no	 response is received within the deadline, a warning is logged
       that the mail may be delivered multiple times.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_data_init_timeout (default: 120s)
       The  SMTP  client time limit for sending the SMTP DATA command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_data_xfer_timeout (default: 180s)
       The  SMTP client time limit for sending the SMTP message content.  When
       the connection makes no progress for more than  $smtp_data_xfer_timeout
       seconds the Postfix SMTP client terminates the transfer.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_defer_if_no_mx_address_found (default: no)
       Defer mail delivery when no MX record resolves to an IP address.

       The default (no) is to return the mail  as  undeliverable.  With	 older
       Postfix	versions  the  default	was to keep trying to deliver the mail
       until someone fixed the MX record or until the mail was too old.

       Note: Postfix always ignores MX records with equal or worse  preference
       than the local MTA itself.

       This feature is available in Postfix 2.1 and later.

smtp_destination_concurrency_limit    (default:	  $default_destination_concur‐
       rency_limit)
       The maximal number of parallel deliveries to the same  destination  via
       the  smtp  message  delivery  transport.	 This limit is enforced by the
       queue manager. The message delivery transport name is the  first	 field
       in the entry in the master.cf file.

smtp_destination_recipient_limit     (default:	  $default_destination_recipi‐
       ent_limit)
       The maximal number of recipients	 per  message  for  the	 smtp  message
       delivery	 transport.  This  limit is enforced by the queue manager. The
       message delivery transport name is the first field in the entry in  the
       master.cf file.

       Setting this parameter to a value of 1 changes the meaning of smtp_des‐
       tination_concurrency_limit from concurrency per domain into concurrency
       per recipient.

smtp_discard_ehlo_keyword_address_maps (default: empty)
       Lookup  tables,	indexed	 by  the remote SMTP server address, with case
       insensitive lists of EHLO keywords (pipelining, starttls,  auth,	 etc.)
       that  the  Postfix  SMTP client will ignore in the EHLO response from a
       remote SMTP server. See smtp_discard_ehlo_keywords for details. The ta‐
       ble  is	not  indexed  by  hostname  for	 consistency  with  smtpd_dis‐
       card_ehlo_keyword_address_maps.

       This feature is available in Postfix 2.2 and later.

smtp_discard_ehlo_keywords (default: empty)
       A case insensitive list of EHLO keywords (pipelining,  starttls,	 auth,
       etc.)  that  the	 Postfix  SMTP client will ignore in the EHLO response
       from a remote SMTP server.

       This feature is available in Postfix 2.2 and later.

       Notes:

       ·      Specify the silent-discard pseudo keyword to prevent this action
	      from being logged.

       ·      Use  the	smtp_discard_ehlo_keyword_address_maps feature to dis‐
	      card EHLO keywords selectively.

smtp_dns_resolver_options (default: empty)
       DNS Resolver options for the Postfix SMTP client.  Specify zero or more
       of  the	following  options,  separated by comma or whitespace.	Option
       names are case-sensitive. Some options refer to domain names  that  are
       specified in the file /etc/resolv.conf or equivalent.

       res_defnames
	      Append  the current domain name to single-component names (those
	      that do not contain a "." character). This can produce incorrect
	      results, and is the hard-coded behavior prior to Postfix 2.8.

       res_dnsrch
	      Search  for  host	 names	in  the	 current  domain and in parent
	      domains. This can produce incorrect results and is therefore not
	      recommended.

       This feature is available in Postfix 2.8 and later.

smtp_enforce_tls (default: no)
       Enforcement  mode: require that remote SMTP servers use TLS encryption,
       and never send mail in the clear.  This also requires that  the	remote
       SMTP  server hostname matches the information in the remote server cer‐
       tificate, and that the remote SMTP server certificate was issued	 by  a
       CA  that	 is  trusted  by  the  Postfix SMTP client. If the certificate
       doesn't verify or the hostname doesn't match, delivery is deferred  and
       mail stays in the queue.

       The  server  hostname is matched against all names provided as dNSNames
       in the SubjectAlternativeName.  If no dNSNames are specified, the  Com‐
       monName	 is   checked.	  The	behavior   may	be  changed  with  the
       smtp_tls_enforce_peername option.

       This option is useful only if you are definitely	 sure  that  you  will
       only  connect to servers that support RFC 2487 _and_ that provide valid
       server certificates.  Typical use is for clients that  send  all	 their
       email to a dedicated mailhub.

       This  feature  is  available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtp_tls_security_level instead.

smtp_fallback_relay (default: $fallback_relay)
       Optional list of relay hosts for SMTP destinations that can't be	 found
       or that are unreachable. With Postfix 2.2 and earlier this parameter is
       called fallback_relay.

       By default, mail is returned to the sender when a  destination  is  not
       found, and delivery is deferred when a destination is unreachable.

       The  fallback relays must be SMTP destinations. Specify a domain, host,
       host:port, [host]:port, [address] or [address]:port;  the  form	[host]
       turns off MX lookups.  If you specify multiple SMTP destinations, Post‐
       fix will try them in the specified order.

       To prevent mailer loops between MX hosts and fall-back  hosts,  Postfix
       version 2.2 and later will not use the fallback relays for destinations
       that it is MX host for (assuming DNS lookup is turned on).

smtp_generic_maps (default: empty)
       Optional lookup tables that  perform  address  rewriting	 in  the  SMTP
       client,	typically to transform a locally valid address into a globally
       valid address when sending mail across the Internet.   This  is	needed
       when  the local machine does not have its own Internet domain name, but
       uses something like localdomain.local instead.

       The table format and lookups are documented in generic(5); examples are
       shown in the ADDRESS_REWRITING_README and STANDARD_CONFIGURATION_README
       documents.

       This feature is available in Postfix 2.2 and later.

smtp_header_checks (default: empty)
       Restricted header_checks(5) tables for the Postfix SMTP client.	 These
       tables are searched while mail is being delivered.  Actions that change
       the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_helo_name (default: $myhostname)
       The hostname to send in the SMTP EHLO or HELO command.

       The default value is the	 machine  hostname.   Specify  a  hostname  or
       [ip.add.re.ss].

       This  information  can  be  specified  in the main.cf file for all SMTP
       clients, or it can be specified in the master.cf file  for  a  specific
       client, for example:

	   /usr/local/etc/postfix/master.cf:
	       mysmtp ... smtp -o smtp_helo_name=foo.bar.com

       This feature is available in Postfix 2.0 and later.

smtp_helo_timeout (default: 300s)
       The  SMTP  client  time limit for sending the HELO or EHLO command, and
       for receiving the initial server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_host_lookup (default: dns)
       What  mechanisms	 the  Postfix  SMTP client uses to look up a host's IP
       address.	 This parameter is ignored when DNS lookups are disabled (see:
       disable_dns_lookups).

       Specify one of the following:

       dns    Hosts can be found in the DNS (preferred).

       native Use the native naming service only (nsswitch.conf, or equivalent
	      mechanism).

       dns, native
	      Use the native service for hosts not found in the DNS.

       This feature is available in Postfix 2.1 and later.

smtp_line_length_limit (default: 990)
       The maximal length of message header and body lines that	 Postfix  will
       send via SMTP.  Longer lines are broken by inserting "<CR><LF><SPACE>".
       This minimizes the damage to MIME formatted mail.

       By default, the line length is limited to 990 characters, because  some
       server implementations cannot receive mail with long lines.

smtp_mail_timeout (default: 300s)
       The  SMTP  client time limit for sending the MAIL FROM command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_mime_header_checks (default: empty)
       Restricted  mime_header_checks(5)  tables  for the Postfix SMTP client.
       These tables are searched while mail is being delivered.	 Actions  that
       change the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_mx_address_limit (default: 5)
       The  maximal number of MX (mail exchanger) IP addresses that can result
       from mail exchanger lookups, or zero (no limit). Prior to Postfix  ver‐
       sion 2.3, this limit was disabled by default.

       This feature is available in Postfix 2.1 and later.

smtp_mx_session_limit (default: 2)
       The  maximal number of SMTP sessions per delivery request before giving
       up or delivering to a fall-back relay host, or zero  (no	 limit).  This
       restriction  ignores  sessions  that  fail to complete the SMTP initial
       handshake (Postfix version 2.2 and earlier) or that  fail  to  complete
       the EHLO and TLS handshake (Postfix version 2.3 and later).

       This feature is available in Postfix 2.1 and later.

smtp_nested_header_checks (default: empty)
       Restricted  nested_header_checks(5) tables for the Postfix SMTP client.
       These tables are searched while mail is being delivered.	 Actions  that
       change the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_never_send_ehlo (default: no)
       Never  send  EHLO  at  the  start  of  an  SMTP	session.  See also the
       smtp_always_send_ehlo parameter.

smtp_pix_workaround_delay_time (default: 10s)
       How long the Postfix SMTP client pauses before sending  ".<CR><LF>"  in
       order to work around the PIX firewall "<CR><LF>.<CR><LF>" bug.

       Choosing	 a too short time makes this workaround ineffective when send‐
       ing large messages over slow network connections.

smtp_pix_workaround_maps (default: empty)
       Lookup tables, indexed by the remote SMTP server address, with per-des‐
       tination	 workarounds  for  CISCO  PIX firewall bugs.  The table is not
       indexed	by  hostname  for  consistency	 with	smtp_discard_ehlo_key‐
       word_address_maps.

       This feature is available in Postfix 2.4 and later.

smtp_pix_workaround_threshold_time (default: 500s)
       How  long a message must be queued before the Postfix SMTP client turns
       on the PIX firewall "<CR><LF>.<CR><LF>"	bug  workaround	 for  delivery
       through firewalls with "smtp fixup" mode turned on.

       By  default,  the  workaround is turned off for mail that is queued for
       less than 500 seconds. In  other	 words,	 the  workaround  is  normally
       turned off for the first delivery attempt.

       Specify 0 to enable the PIX firewall "<CR><LF>.<CR><LF>" bug workaround
       upon the first delivery attempt.

smtp_pix_workarounds (default: disable_esmtp, delay_dotcrlf)
       A list that specifies zero or more workarounds for CISCO	 PIX  firewall
       bugs.  These  workarounds  are  implemented by the Postfix SMTP client.
       Workaround names are separated by comma or space, and are case insensi‐
       tive.   This  parameter	setting	 can be overruled with per-destination
       smtp_pix_workaround_maps settings.

       delay_dotcrlf
	      Insert a delay before sending ".<CR><LF>" after the end  of  the
	      message  content.	  The  delay  is subject to the smtp_pix_work‐
	      around_delay_time and smtp_pix_workaround_threshold_time parame‐
	      ter settings.

       disable_esmtp
	      Disable all extended SMTP commands: send HELO instead of EHLO.

       This  feature  is  available in Postfix 2.4 and later. The default set‐
       tings are backwards compatible with earlier Postfix versions.

smtp_quit_timeout (default: 300s)
       The SMTP client time limit  for	sending	 the  QUIT  command,  and  for
       receiving the server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_quote_rfc821_envelope (default: yes)
       Quote addresses in SMTP MAIL FROM and RCPT TO commands as  required  by
       RFC 2821. This includes putting quotes around an address localpart that
       ends in ".".

       The default is to comply with RFC 2821. If you have to send mail	 to  a
       broken SMTP server, configure a special SMTP client in master.cf:

	   /usr/local/etc/postfix/master.cf:
	       broken-smtp . . . smtp -o smtp_quote_rfc821_envelope=no

       and  route  mail	 for  the destination in question to the "broken-smtp"
       message delivery with a transport(5) table.

       This feature is available in Postfix 2.1 and later.

smtp_randomize_addresses (default: yes)
       Randomize the order of equal-preference MX host addresses.  This	 is  a
       performance feature of the Postfix SMTP client.

smtp_rcpt_timeout (default: 300s)
       The  SMTP  client  time limit for sending the SMTP RCPT TO command, and
       for receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_reply_filter (default: empty)
       A mechanism to transform replies from remote SMTP servers one line at a
       time.  This is a last-resort tool to work around	 server	 replies  that
       break  inter-operability	 with  the  Postfix  SMTP  client.  Other uses
       involve	fault  injection  to  test  Postfix's  handling	  of   invalid
       responses.

       Notes:

       ·      In  the case of a multi-line reply, the Postfix SMTP client uses
	      the final reply line's numerical SMTP reply  code	 and  enhanced
	      status code.

       ·      The  numerical  SMTP  reply code (XYZ) takes precedence over the
	      enhanced status code (X.Y.Z).  When  the	enhanced  status  code
	      initial digit differs from the SMTP reply code initial digit, or
	      when no enhanced status code is present, the Postfix SMTP client
	      uses a generic enhanced status code (X.0.0) instead.

       Specify the name of a "type:table" lookup table. The search string is a
       single SMTP reply line as received from the remote SMTP server,	except
       that the trailing <CR><LF> are removed.

       Examples:

       /usr/local/etc/postfix/main.cf:
	   smtp_reply_filter = pcre:$config_directory/reply_filter

       /usr/local/etc/postfix/reply_filter:
	   # Transform garbage into "250-filler..." so that it looks like
	   # one line from a multi-line reply. It does not matter what we
	   # substitute here as long it has the right syntax.  The Postfix
	   # SMTP client will use the final line's numerical SMTP reply
	   # code and enhanced status code.
	   !/^([2-5][0-9][0-9]($|[- ]))/ 250-filler for garbage

       This feature is available in Postfix 2.7.

smtp_rset_timeout (default: 20s)
       The  SMTP  client  time	limit  for  sending  the RSET command, and for
       receiving the server response. The SMTP client sends RSET in  order  to
       finish a recipient address probe, or to verify that a cached session is
       still usable.

       This feature is available in Postfix 2.1 and later.

smtp_sasl_auth_cache_name (default: empty)
       An optional table to prevent repeated SASL authentication failures with
       the same remote SMTP server hostname, username and password. Each table
       (key, value) pair contains a server name, a username and password,  and
       the full server response. This information is stored when a remote SMTP
       server rejects an authentication attempt with a	535  reply  code.   As
       long  as the smtp_sasl_password_maps information does no change, and as
       long as the smtp_sasl_auth_cache_name information does not expire  (see
       smtp_sasl_auth_cache_time)  the Postfix SMTP client avoids SASL authen‐
       tication attempts with the same	server,	 username  and	password,  and
       instead	  bounces    or	  defers   mail	  as   controlled   with   the
       smtp_sasl_auth_soft_bounce configuration parameter.

       Use  a  per-destination	delivery  concurrency  of  1   (for   example,
       "smtp_destination_concurrency_limit  =  1",  "relay_destination_concur‐
       rency_limit = 1", etc.), otherwise multiple delivery agents may experi‐
       ence a login failure at the same time.

       The  table  must	 be  accessed via the proxywrite service, i.e. the map
       name must start with "proxy:". The table should	be  stored  under  the
       directory specified with the data_directory parameter.

       This  feature  uses  cryptographic  hashing to protect plain-text pass‐
       words, and requires that Postfix is compiled with TLS support.

       Example:

       smtp_sasl_auth_cache_name = proxy:btree:/var/lib/postfix/sasl_auth_cache

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_cache_time (default: 90d)
       The maximal age of an  smtp_sasl_auth_cache_name	 entry	before	it  is
       removed.

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix SMTP client.  By default, the
       Postfix SMTP client uses no authentication.

       Example:

       smtp_sasl_auth_enable = yes

smtp_sasl_auth_soft_bounce (default: yes)
       When a remote SMTP server rejects a SASL authentication request with  a
       535  reply code, defer mail delivery instead of returning mail as unde‐
       liverable. The latter behavior was hard-coded prior to Postfix  version
       2.5.

       Note: the setting "yes" overrides the global soft_bounce parameter, but
       the setting "no" does not.

       Example:

       # Default as of Postfix 2.5
       smtp_sasl_auth_soft_bounce = yes
       # The old hard-coded default
       smtp_sasl_auth_soft_bounce = no

       This feature is available in Postfix 2.5 and later.

smtp_sasl_mechanism_filter (default: empty)
       If non-empty, a Postfix SMTP client filter for the remote SMTP server's
       list of offered SASL mechanisms.	 Different client and server implemen‐
       tations may support different mechanism lists. By default, the  Postfix
       SMTP  client  will  use	the  intersection of the two. smtp_sasl_mecha‐
       nism_filter further restricts what server mechanisms  the  client  will
       take into consideration.

       Specify	mechanism  names, "/file/name" patterns or "type:table" lookup
       tables.	The  right-hand	 side  result  from  "type:table"  lookups  is
       ignored.	 Specify "!pattern" to exclude a mechanism name from the list.
       The form "!/file/name" is supported only in  Postfix  version  2.4  and
       later.

       This feature is available in Postfix 2.2 and later.

       Examples:

       smtp_sasl_mechanism_filter = plain, login
       smtp_sasl_mechanism_filter = $config_directory/smtp_mechs
       smtp_sasl_mechanism_filter = !gssapi, !login, static:rest

smtp_sasl_password_maps (default: empty)
       Optional SMTP client lookup tables with one username:password entry per
       remote hostname or domain,  or  sender  address	when  sender-dependent
       authentication  is  enabled.   If  no username:password entry is found,
       then the Postfix SMTP client will not attempt to	 authenticate  to  the
       remote host.

       The  Postfix  SMTP client opens the lookup table before going to chroot
       jail, so you can leave the password file in /usr/local/etc/postfix.

smtp_sasl_path (default: empty)
       Implementation-specific information that the Postfix SMTP client passes
       through	to  the	 SASL  plug-in	implementation	that  is selected with
       smtp_sasl_type.	Typically this specifies the name of  a	 configuration
       file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

smtp_sasl_security_options (default: noplaintext, noanonymous)
       Postfix	SMTP  client SASL security options; as of Postfix 2.3 the list
       of available features depends on the SASL client implementation that is
       selected with smtp_sasl_type.

       The  following  security features are defined for the cyrus client SASL
       implementation:

       Specify zero or more of the following:

       noplaintext
	      Disallow methods that use plaintext passwords.

       noactive
	      Disallow methods subject to active (non-dictionary) attack.

       nodictionary
	      Disallow methods subject to passive (dictionary) attack.

       noanonymous
	      Disallow methods that allow anonymous authentication.

       mutual_auth
	      Only allow  methods  that	 provide  mutual  authentication  (not
	      available with SASL version 1).

       Example:

       smtp_sasl_security_options = noplaintext

smtp_sasl_tls_security_options (default: $smtp_sasl_security_options)
       The  SASL  authentication security options that the Postfix SMTP client
       uses for TLS encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtp_sasl_tls_verified_security_options	    (default:	  $smtp_sasl_tls_secu‐
       rity_options)
       The  SASL  authentication security options that the Postfix SMTP client
       uses for TLS encrypted SMTP sessions with a  verified  server  certifi‐
       cate.

       When  mail  is  sent  to the public MX host for the recipient's domain,
       server certificates are by default optional, and delivery proceeds even
       if  certificate	verification fails. For delivery via a submission ser‐
       vice that requires SASL authentication, it may be appropriate  to  send
       plaintext  passwords only when the connection to the server is strongly
       encrypted and the server identity is verified.

       The smtp_sasl_tls_verified_security_options parameter makes it possible
       to  only	 enable	 plaintext  mechanisms when a secure connection to the
       server is available. Submission servers subject	to  this  policy  must
       either  have  verifiable	 certificates  or offer suitable non-plaintext
       SASL mechanisms.

       This feature is available in Postfix 2.6 and later.

smtp_sasl_type (default: cyrus)
       The SASL plug-in type that the  Postfix	SMTP  client  should  use  for
       authentication.	 The available types are listed with the "postconf -A"
       command.

       This feature is available in Postfix 2.3 and later.

smtp_send_xforward_command (default: no)
       Send the non-standard XFORWARD command when  the	 Postfix  SMTP	server
       EHLO response announces XFORWARD support.

       This  allows  an	 "smtp" delivery agent, used for injecting mail into a
       content filter, to forward the name, address, protocol and HELO name of
       the  original  client to the content filter and downstream queuing SMTP
       server. This can produce more useful logging than  localhost[127.0.0.1]
       etc.

       This feature is available in Postfix 2.1 and later.

smtp_sender_dependent_authentication (default: no)
       Enable sender-dependent authentication in the Postfix SMTP client; this
       is available only with SASL authentication, and disables	 SMTP  connec‐
       tion  caching  to  ensure that mail from different senders will use the
       appropriate credentials.

       This feature is available in Postfix 2.3 and later.

smtp_skip_4xx_greeting (default: yes)
       Skip SMTP servers that greet with a 4XX status code (go away, try again
       later).

       By   default,  Postfix  moves  on  the  next  mail  exchanger.  Specify
       "smtp_skip_4xx_greeting = no" if Postfix should defer delivery  immedi‐
       ately.

       This  feature  is  available in Postfix 2.0 and earlier.	 Later Postfix
       versions always skip SMTP servers that greet with a 4XX status code.

smtp_skip_5xx_greeting (default: yes)
       Skip SMTP servers that greet with a 5XX status code (go	away,  do  not
       try again later).

       By  default,  the Postfix SMTP client moves on the next mail exchanger.
       Specify "smtp_skip_5xx_greeting = no" if Postfix should bounce the mail
       immediately.  The default setting is incorrect, but it is what a lot of
       people expect to happen.

smtp_skip_quit_response (default: yes)
       Do not wait for the response to the SMTP QUIT command.

smtp_starttls_timeout (default: 300s)
       Time limit for Postfix SMTP client write and read operations during TLS
       startup and shutdown handshake procedures.

       This feature is available in Postfix 2.2 and later.

smtp_tls_CAfile (default: empty)
       A  file	containing  CA certificates of root CAs trusted to sign either
       remote SMTP server certificates or intermediate CA certificates.	 These
       are  loaded  into  memory  before  the smtp(8) client enters the chroot
       jail.  If  the  number  of  trusted  roots  is  large,  consider	 using
       smtp_tls_CApath	instead,  but  note  that the latter directory must be
       present in the chroot jail if the smtp(8) client is chrooted. This file
       may  also be used to augment the client certificate trust chain, but it
       is  best	 to  include  all  the	required  certificates	 directly   in
       $smtp_tls_cert_file.

       Specify	"tls_append_default_CA = no" to prevent Postfix from appending
       the system-supplied default CAs and trusting third-party certificates.

       Example:

       smtp_tls_CAfile = $config_directory/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_CApath (default: empty)
       Directory with PEM format certificate authority certificates  that  the
       Postfix	SMTP  client  uses to verify a remote SMTP server certificate.
       Don't forget to create the necessary "hash" links  with,	 for  example,
       "$OPENSSL_HOME/bin/c_rehash /usr/local/etc/postfix/certs".

       To  use	this option in chroot mode, this directory (or a copy) must be
       inside the chroot jail.

       Specify "tls_append_default_CA = no" to prevent Postfix from  appending
       the system-supplied default CAs and trusting third-party certificates.

       Example:

       smtp_tls_CApath = $config_directory/certs

       This feature is available in Postfix 2.2 and later.

smtp_tls_block_early_mail_reply (default: no)
       Try  to detect a mail hijacking attack based on a TLS protocol vulnera‐
       bility (CVE-2009-3555), where  an  attacker  prepends  malicious	 HELO,
       MAIL,  RCPT,  DATA  commands to a Postfix SMTP client TLS session.  The
       attack would succeed with non-Postfix SMTP servers that	reply  to  the
       malicious HELO, MAIL, RCPT, DATA commands after negotiating the Postfix
       SMTP client TLS session.

       This feature is available in Postfix 2.7.

smtp_tls_cert_file (default: empty)
       File with the Postfix SMTP client RSA certificate in PEM format.	  This
       file  may  also	contain	 the  Postfix SMTP client private RSA key, and
       these may be the same as the Postfix SMTP server	 RSA  certificate  and
       key file.

       Do not configure client certificates unless you must present client TLS
       certificates to one or more servers. Client certificates are  not  usu‐
       ally  needed,  and  can cause problems in configurations that work well
       without them. The recommended setting is to let the defaults stand:

	   smtp_tls_cert_file =
	   smtp_tls_key_file =
	   smtp_tls_dcert_file =
	   smtp_tls_dkey_file =
	   smtp_tls_eccert_file =
	   smtp_tls_eckey_file =

       The best way to use the default settings is to comment  out  the	 above
       parameters in main.cf if present.

       To  enable  remote  SMTP servers to verify the Postfix SMTP client cer‐
       tificate, the issuing CA certificates must be  made  available  to  the
       server. You should include the required certificates in the client cer‐
       tificate file, the client certificate first,  then  the	issuing	 CA(s)
       (bottom-up order).

       Example: the certificate for "client.example.com" was issued by "inter‐
       mediate CA" which itself has a certificate issued by "root CA".	Create
       the  client.pem	file  with  "cat  client_cert.pem  intermediate_CA.pem
       root_CA.pem > client.pem".

       If you also want to verify remote SMTP server  certificates  issued  by
       these  CAs,  you can add the CA certificates to the smtp_tls_CAfile, in
       which case it is not necessary to have them in the  smtp_tls_cert_file,
       smtp_tls_dcert_file or smtp_tls_eccert_file.

       A certificate supplied here must be usable as an SSL client certificate
       and hence pass the "openssl verify -purpose sslclient ..." test.

       Example:

       smtp_tls_cert_file = $config_directory/client.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_cipherlist (default: empty)
       Obsolete Postfix < 2.3 control for the Postfix SMTP client  TLS	cipher
       list. As this feature applies to all TLS security levels, it is easy to
       create inter-operability problems  by  choosing	a  non-default	cipher
       list.  Do  not  use a non-default TLS cipher list on hosts that deliver
       email to the public Internet: you will  be  unable  to  send  email  to
       servers	that  only support the ciphers you exclude. Using a restricted
       cipher list may be more appropriate for an internal MTA, where one  can
       exert  some  control  over  the	TLS  software and settings of the peer
       servers.

       Note: do not use "" quotes around the parameter value.

       This feature is available in Postfix version 2.2. It is not  used  with
       Postfix 2.3 and later; use smtp_tls_mandatory_ciphers instead.

smtp_tls_ciphers (default: export)
       The minimum TLS cipher grade that the Postfix SMTP client will use with
       opportunistic	TLS    encryption.    Cipher	types	 listed	    in
       smtp_tls_exclude_ciphers	 are  excluded from the base definition of the
       selected cipher grade.  The  default  value  "export"  ensures  maximum
       inter-operability.  Because  encryption	is optional, stronger controls
       are not appropriate, and this setting SHOULD NOT be changed unless  the
       change is essential.

       When   TLS   is	 mandatory   the   cipher  grade  is  chosen  via  the
       smtp_tls_mandatory_ciphers configuration parameter, see there for  syn‐
       tax details. See smtp_tls_policy_maps for information on how to config‐
       ure ciphers on a per-destination basis.

       Example:
       smtp_tls_ciphers = export

       This feature is available in Postfix 2.6 and later. With earlier	 Post‐
       fix  releases  only  the smtp_tls_mandatory_ciphers parameter is imple‐
       mented, and opportunistic TLS always uses "export" or better (i.e. all)
       ciphers.

smtp_tls_dcert_file (default: empty)
       File  with the Postfix SMTP client DSA certificate in PEM format.  This
       file may also contain the Postfix SMTP client private DSA key.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_dcert_file = $config_directory/client-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_dkey_file (default: $smtp_tls_dcert_file)
       File with the Postfix SMTP client DSA private key in PEM format.	  This
       file  may be combined with the Postfix SMTP client DSA certificate file
       specified with $smtp_tls_dcert_file.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtp_tls_eccert_file (default: empty)
       File with the Postfix SMTP client  ECDSA	 certificate  in  PEM  format.
       This file may also contain the Postfix SMTP client ECDSA private key.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_eccert_file = $config_directory/ecdsa-ccert.pem

       This  feature  is  available  in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

smtp_tls_eckey_file (default: $smtp_tls_eccert_file)
       File with the Postfix SMTP client ECDSA	private	 key  in  PEM  format.
       This  file  may be combined with the Postfix SMTP client ECDSA certifi‐
       cate file specified with $smtp_tls_eccert_file.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.6 and  later,  when  Postfix  is
       compiled and linked with OpenSSL 1.0.0 or later.

smtp_tls_enforce_peername (default: yes)
       With  mandatory	TLS  encryption,  require  that the remote SMTP server
       hostname matches the information in the remote SMTP server certificate.
       As  of  RFC 2487 the requirements for hostname checking for MTA clients
       are not specified.

       This option can be set to "no" to disable strict	 peer  name  checking.
       This  setting  has  no  effect  on sessions that are controlled via the
       smtp_tls_per_site table.

       Disabling the hostname verification can make sense in  closed  environ‐
       ment where special CAs are created.  If not used carefully, this option
       opens the danger of a "man-in-the-middle"  attack  (the	CommonName  of
       this attacker will be logged).

       This  feature  is  available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtp_tls_security_level instead.

smtp_tls_exclude_ciphers (default: empty)
       List of ciphers or cipher types to exclude from the Postfix SMTP client
       cipher  list  at	 all  TLS  security  levels.  This  is	not an OpenSSL
       cipherlist, it is a simple list separated by whitespace and/or  commas.
       The  elements  are a single cipher, or one or more "+" separated cipher
       properties, in which case only ciphers matching all the properties  are
       excluded.

       Examples (some of these will cause problems):

	   smtp_tls_exclude_ciphers = aNULL
	   smtp_tls_exclude_ciphers = MD5, DES
	   smtp_tls_exclude_ciphers = DES+MD5
	   smtp_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
	   smtp_tls_exclude_ciphers = kEDH+aRSA

       The  first  setting,  disables anonymous ciphers. The next setting dis‐
       ables ciphers that use the MD5 digest algorithm	or  the	 (single)  DES
       encryption  algorithm.  The  next setting disables ciphers that use MD5
       and  DES	 together.   The  next	setting	 disables  the	 two   ciphers
       "AES256-SHA" and "DES-CBC3-MD5". The last setting disables ciphers that
       use "EDH" key exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtp_tls_fingerprint_cert_match (default: empty)
       List of acceptable remote SMTP server certificate fingerprints for  the
       "fingerprint"  TLS  security  level  (smtp_tls_security_level = finger‐
       print). At this security level, certificate authorities are  not	 used,
       and  certificate expiration times are ignored. Instead, server certifi‐
       cates are verified directly via their "fingerprint". The fingerprint is
       a  message  digest  of  the server certificate. The digest algorithm is
       selected via the smtp_tls_fingerprint_digest parameter.

       When an smtp_tls_policy_maps table entry	 specifies  the	 "fingerprint"
       security	 level,	 any "match" attributes in that entry specify the list
       of valid fingerprints for the corresponding destination. Multiple  fin‐
       gerprints  can  be  combined  with  a  "|"  delimiter in a single match
       attribute, or multiple match attributes can be employed.

       Example: Certificate fingerprint verification  with  internal  mailhub.
       Two  matching  fingerprints  are	 listed. The relayhost may be multiple
       physical hosts behind a load-balancer, each with its own private/public
       key  and self-signed certificate. Alternatively, a single relayhost may
       be in the process of switching from one set of private/public  keys  to
       another, and both keys are trusted just prior to the transition.

	   relayhost = [mailhub.example.com]
	   smtp_tls_security_level = fingerprint
	   smtp_tls_fingerprint_digest = md5
	   smtp_tls_fingerprint_cert_match =
	       3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
	       EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       Example:	 Certificate  fingerprint  verification with selected destina‐
       tions.  As in the example above, we show two matching fingerprints:

	   /usr/local/etc/postfix/main.cf:
	       smtp_tls_policy_maps = hash:$config_directory/tls_policy
	       smtp_tls_fingerprint_digest = md5

	   /usr/local/etc/postfix/tls_policy:
	       example.com     fingerprint
		   match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
		   match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.5 and later.

smtp_tls_fingerprint_digest (default: md5)
       The message digest algorithm used to construct remote SMTP server  cer‐
       tificate	  fingerprints.	  At  the  "fingerprint"  TLS  security	 level
       (smtp_tls_security_level = fingerprint), the server certificate is ver‐
       ified by directly matching its fingerprint. The fingerprint is the mes‐
       sage digest of the server certificate  using  the  selected  algorithm.
       With  a digest algorithm resistant to "second pre-image" attacks, it is
       not feasible to create a new public key and a matching certificate that
       has the same fingerprint.

       The  default  algorithm	is  md5; this is consistent with the backwards
       compatible setting of the digest used to verify client certificates  in
       the SMTP server.

       The  best practice algorithm is now sha1. Recent advances in hash func‐
       tion cryptanalysis have led to md5 being deprecated in favor  of	 sha1.
       However,	 as  long  as  there  are  no known "second pre-image" attacks
       against md5, its use in this context can still be considered safe.

       While additional digest algorithms are often available  with  OpenSSL's
       libcrypto, only those used by libssl in SSL cipher suites are available
       to Postfix. For now this means just md5 or sha1.

       To find the fingerprint of a specific certificate file, with a specific
       digest algorithm, run:

	   $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The  text  to  the  right  of "=" sign is the desired fingerprint.  For
       example:

	   $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
	   SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       This feature is available in Postfix 2.5 and later.

smtp_tls_key_file (default: $smtp_tls_cert_file)
       File with the Postfix SMTP client RSA private key in PEM format.	  This
       file  may be combined with the Postfix SMTP client RSA certificate file
       specified with $smtp_tls_cert_file.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       Example:

       smtp_tls_key_file = $smtp_tls_cert_file

       This feature is available in Postfix 2.2 and later.

smtp_tls_loglevel (default: 0)
       Enable additional Postfix SMTP client logging of	 TLS  activity.	  Each
       logging	level  also includes the information that is logged at a lower
       logging level.

	      0 Disable logging of TLS activity.

	      1 Log TLS handshake and certificate information.

	      2 Log levels during TLS negotiation.

	      3 Log hexadecimal and ASCII dump of TLS negotiation process.

	      4 Log hexadecimal and ASCII dump of complete transmission	 after
	      STARTTLS.

       Use "smtp_tls_loglevel = 3" only in case of problems. Use of loglevel 4
       is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtp_tls_mandatory_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP client will use with
       mandatory  TLS  encryption.  The default value "medium" is suitable for
       most destinations with which you may want to enforce TLS, and is beyond
       the  reach  of  today's cryptanalytic methods. See smtp_tls_policy_maps
       for information on how to configure ciphers on a per-destination basis.

       The following cipher grades are supported:

       export Enable "EXPORT" grade or better OpenSSL ciphers.	 This  is  the
	      default  for opportunistic encryption. It is not recommended for
	      mandatory encryption unless you must enforce TLS with "crippled"
	      peers.   The   underlying	  cipherlist   is  specified  via  the
	      tls_export_cipherlist configuration  parameter,  which  you  are
	      strongly encouraged to not change.

       low    Enable  "LOW"  grade or better OpenSSL ciphers.  This setting is
	      only appropriate for  internal  mail  servers.   The  underlying
	      cipherlist is specified via the tls_low_cipherlist configuration
	      parameter, which you are strongly encouraged to not change.

       medium Enable "MEDIUM" grade or better OpenSSL ciphers.	The underlying
	      cipherlist is specified via the tls_medium_cipherlist configura‐
	      tion parameter, which you are strongly encouraged to not change.

       high   Enable only "HIGH" grade OpenSSL ciphers.	 This setting  may  be
	      appropriate  when	 all mandatory TLS destinations (e.g. when all
	      mail is routed to a suitably capable relayhost) support at least
	      one  "HIGH" grade cipher. The underlying cipherlist is specified
	      via the tls_high_cipherlist configuration parameter,  which  you
	      are strongly encouraged to not change.

       null   Enable  only the "NULL" OpenSSL ciphers, these provide authenti‐
	      cation without encryption.  This setting is only appropriate  in
	      the  rare case that all servers are prepared to use NULL ciphers
	      (not normally enabled in TLS servers). A plausible  use-case  is
	      an LMTP server listening on a UNIX-domain socket that is config‐
	      ured to support "NULL" ciphers.  The  underlying	cipherlist  is
	      specified	 via  the tls_null_cipherlist configuration parameter,
	      which you are strongly encouraged to not change.

       The underlying cipherlists for grades other than "null" include	anony‐
       mous  ciphers,  but these are automatically filtered out if the Postfix
       SMTP client is configured to verify server certificates.	 You are  very
       unlikely	 to  need to take any steps to exclude anonymous ciphers, they
       are excluded automatically as necessary.	 If you must exclude anonymous
       ciphers	at  the	 "may"	or "encrypt" security levels, when the Postfix
       SMTP  client  does   not	  need	 or   use   peer   certificates,   set
       "smtp_tls_exclude_ciphers  =  aNULL". To exclude anonymous ciphers only
       when TLS is enforced, set "smtp_tls_mandatory_exclude_ciphers = aNULL".

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_exclude_ciphers (default: empty)
       Additional list of ciphers or cipher types to  exclude  from  the  SMTP
       client cipher list at mandatory TLS security levels. This list works in
       addition to the exclusions listed  with	smtp_tls_exclude_ciphers  (see
       there for syntax details).

       Starting with Postfix 2.6, the mandatory cipher exclusions can be spec‐
       ified  on  a  per-destination  basis  via  the  TLS  policy   "exclude"
       attribute. See smtp_tls_policy_maps for notes and examples.

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_protocols (default: SSLv3, TLSv1)
       List  of	 SSL/TLS  protocols that the Postfix SMTP client will use with
       mandatory TLS encryption.  In  main.cf  the  values  are	 separated  by
       whitespace, commas or colons. In the policy table "protocols" attribute
       (see smtp_tls_policy_maps) the only valid separator is colon. An	 empty
       value  means allow all protocols. The valid protocol names, (see \fBfB‐
       SSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1".

       With Postfix >= 2.5 the parameter syntax is expanded to support	proto‐
       col  exclusions.	 One  can  now	explicitly  exclude  SSLv2  by setting
       "smtp_tls_mandatory_protocols = !SSLv2".	 To  exclude  both  SSLv2  and
       SSLv3  set "smtp_tls_mandatory_protocols = !SSLv2, !SSLv3". Listing the
       protocols to include, rather than protocols to exclude, is  still  sup‐
       ported; use the form you find more intuitive.

       Since  SSL  version  2  has known protocol weaknesses and is now depre‐
       cated, the default  setting  excludes  "SSLv2".	 This  means  that  by
       default, SSL version 2 will not be used at the "encrypt" security level
       and higher.

       See  the	 documentation	of  the	 smtp_tls_policy_maps  parameter   and
       TLS_README for more information about security levels.

       Example:

       smtp_tls_mandatory_protocols = TLSv1
       # Alternative form with Postfix >= 2.5:
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.3 and later.

smtp_tls_note_starttls_offer (default: no)
       Log the hostname of a remote SMTP server that offers STARTTLS, when TLS
       is not already enabled for that server.

       The logfile record looks like:

       postfix/smtp[pid]:  Host offered STARTTLS: [name.of.host]

       This feature is available in Postfix 2.2 and later.

smtp_tls_per_site (default: empty)
       Optional lookup tables with the Postfix SMTP client TLS usage policy by
       next-hop	 destination  and  by  remote SMTP server hostname.  When both
       lookups succeed, the more specific per-site policy  (NONE,  MUST,  etc)
       overrides  the  less  specific  one (MAY), and the more secure per-site
       policy (MUST, etc) overrides the less secure one (NONE).	 With  Postfix
       2.3   and   later   smtp_tls_per_site   is  strongly  discouraged:  use
       smtp_tls_policy_maps instead.

       Use of the bare hostname as the per-site table lookup key  is  discour‐
       aged.  Always  use  the full destination nexthop (enclosed in [] with a
       possible ":port" suffix). A recipient domain  or	 MX-enabled  transport
       next-hop	 with  no  port	 suffix	 may look like a bare hostname, but is
       still a suitable destination.

       Specify a next-hop destination or  server  hostname  on	the  left-hand
       side;  no wildcards are allowed. The next-hop destination is either the
       recipient domain, or the destination specified with a transport(5)  ta‐
       ble, the relayhost parameter, or the relay_transport parameter.	On the
       right hand side specify one of the following keywords:

       NONE   Don't use TLS at all. This overrides a less specific MAY	lookup
	      result from the alternate host or next-hop lookup key, and over‐
	      rides   the   global   smtp_use_tls,    smtp_enforce_tls,	   and
	      smtp_tls_enforce_peername settings.

       MAY    Try  to  use  TLS if the server announces support, otherwise use
	      the unencrypted connection. This has less precedence than a more
	      specific	result	(including  NONE)  from	 the alternate host or
	      next-hop lookup key, and has less precedence than the more  spe‐
	      cific global "smtp_enforce_tls = yes" or "smtp_tls_enforce_peer‐
	      name = yes".

       MUST_NOPEERMATCH
	      Require TLS encryption, but do not require that the remote  SMTP
	      server  hostname	matches	 the  information  in  the remote SMTP
	      server certificate, or that the server certificate was issued by
	      a	 trusted  CA. This overrides a less secure NONE or a less spe‐
	      cific MAY lookup result from  the	 alternate  host  or  next-hop
	      lookup	key,	and   overrides	  the	global	 smtp_use_tls,
	      smtp_enforce_tls and smtp_tls_enforce_peername settings.

       MUST   Require TLS encryption, require  that  the  remote  SMTP	server
	      hostname	matches the information in the remote SMTP server cer‐
	      tificate, and require that the remote  SMTP  server  certificate
	      was  issued  by  a trusted CA. This overrides a less secure NONE
	      and MUST_NOPEERMATCH or a less specific MAY lookup  result  from
	      the  alternate  host  or	next-hop lookup key, and overrides the
	      global smtp_use_tls, smtp_enforce_tls and smtp_tls_enforce_peer‐
	      name settings.

       The above keywords correspond to the "none", "may", "encrypt" and "ver‐
       ify" security levels  for  the  new  smtp_tls_security_level  parameter
       introduced in Postfix 2.3. Starting with Postfix 2.3, and independently
       of how the policy  is  specified,  the  smtp_tls_mandatory_ciphers  and
       smtp_tls_mandatory_protocols  parameters	 apply	when TLS encryption is
       mandatory. Connections  for  which  encryption  is  optional  typically
       enable  all "export" grade and better ciphers (see smtp_tls_ciphers and
       smtp_tls_protocols).

       As long as no secure DNS lookup mechanism is available, false hostnames
       in  MX  or  CNAME responses can change the server hostname that Postfix
       uses for TLS policy lookup and server  certificate  verification.  Even
       with  a	perfect	 match between the server hostname and the server cer‐
       tificate, there is no guarantee that Postfix is connected to the	 right
       server.	 See TLS_README (Closing a DNS loophole with obsolete per-site
       TLS policies) for a possible work-around.

       This feature is available in Postfix 2.2 and later.  With  Postfix  2.3
       and later use smtp_tls_policy_maps instead.

smtp_tls_policy_maps (default: empty)
       Optional lookup tables with the Postfix SMTP client TLS security policy
       by next-hop destination; when a	non-empty  value  is  specified,  this
       overrides the obsolete smtp_tls_per_site parameter.  See TLS_README for
       a more detailed discussion of TLS security levels.

       The TLS policy table is indexed by the full next-hop destination, which
       is  either  the recipient domain, or the verbatim next-hop specified in
       the    transport	   table,    $local_transport,	   $virtual_transport,
       $relay_transport	 or  $default_transport.  This	includes any enclosing
       square brackets and any non-default destination server port suffix. The
       LMTP  socket type prefix (inet: or unix:) is not included in the lookup
       key.

       Only the next-hop domain, or $myhostname	 with  LMTP  over  UNIX-domain
       sockets,	 is used as the nexthop name for certificate verification. The
       port and any enclosing square brackets are used	in  the	 table	lookup
       key, but are not used for server name verification.

       When  the lookup key is a domain name without enclosing square brackets
       or any :port suffix (typically the  recipient  domain),	and  the  full
       domain  is not found in the table, just as with the transport(5) table,
       the parent domain starting with a leading "." is	 matched  recursively.
       This allows one to specify a security policy for a recipient domain and
       all its sub-domains.

       The lookup result is a security level, followed by an optional list  of
       whitespace  and/or  comma separated name=value attributes that override
       related main.cf settings. The TLS security levels in order of  increas‐
       ing security are:

       none   No TLS. No additional attributes are supported at this level.

       may    Opportunistic  TLS.  Since  sending  in the clear is acceptable,
	      demanding stronger than  default	TLS  security  merely  reduces
	      inter-operability. The optional "ciphers", "exclude" and "proto‐
	      cols" attributes (available for opportunistic TLS	 with  Postfix
	      >=       2.6)	  override	 the	   "smtp_tls_ciphers",
	      "smtp_tls_exclude_ciphers" and  "smtp_tls_protocols"  configura‐
	      tion parameters. When opportunistic TLS handshakes fail, Postfix
	      retries the connection with  TLS	disabled.   This  allows  mail
	      delivery to sites with non-interoperable TLS implementations.

       encrypt
	      Mandatory TLS encryption. At this level and higher, the optional
	      "protocols"  attribute  overrides	 the  main.cf  smtp_tls_manda‐
	      tory_protocols parameter, the optional "ciphers" attribute over‐
	      rides the main.cf smtp_tls_mandatory_ciphers parameter, and  the
	      optional	"exclude"  attribute  (Postfix	>=  2.6) overrides the
	      main.cf  smtp_tls_mandatory_exclude_ciphers  parameter.  In  the
	      policy  table,  multiple	protocols  or excluded ciphers must be
	      separated by colons, as attribute values may not contain	white‐
	      space or commas.

       fingerprint
	      Certificate fingerprint verification. Available with Postfix 2.5
	      and later. At this security level, there are no trusted certifi‐
	      cate  authorities. The certificate trust chain, expiration date,
	      ... are not checked. Instead, the optional match	attribute,  or
	      else   the  main.cf  smtp_tls_fingerprint_cert_match  parameter,
	      lists the valid "fingerprints" of the  server  certificate.  The
	      digest  algorithm	 used to calculate the fingerprint is selected
	      by the smtp_tls_fingerprint_digest parameter.  Multiple  finger‐
	      prints  can  be  combined with a "|" delimiter in a single match
	      attribute, or multiple match attributes can be employed. The ":"
	      character	 is  not used as a delimiter as it occurs between each
	      pair of fingerprint (hexadecimal) digits.

       verify Mandatory TLS verification.  At  this  security  level,  DNS  MX
	      lookups  are  trusted to be secure enough, and the name verified
	      in the server certificate is  usually  obtained  indirectly  via
	      unauthenticated  DNS MX lookups.	The optional "match" attribute
	      overrides the main.cf smtp_tls_verify_cert_match	parameter.  In
	      the policy table, multiple match patterns and strategies must be
	      separated by colons.  In practice explicit control over matching
	      is more common with the "secure" policy, described below.

       secure Secure-channel  TLS.  At	this  security	level, DNS MX lookups,
	      though potentially used  to  determine  the  candidate  next-hop
	      gateway  IP  addresses,  are not trusted to be secure enough for
	      TLS peername verification. Instead, the default name verified in
	      the  server  certificate is obtained directly from the next-hop,
	      or is explicitly specified  via  the  optional  match  attribute
	      which  overrides	the main.cf smtp_tls_secure_cert_match parame‐
	      ter. In the policy table, multiple match patterns and strategies
	      must be separated by colons.  The match attribute is most useful
	      when multiple domains are supported by common server, the policy
	      entries  for  additional	domains specify matching rules for the
	      primary domain  certificate.  While  transport  table  overrides
	      routing  the secondary domains to the primary nexthop also allow
	      secure verification, they risk delivery to the wrong destination
	      when  domains  change  hands or are re-assigned to new gateways.
	      With the "match" attribute approach, routing is  not  perturbed,
	      and mail is deferred if verification of a new MX host fails.

       Example:

       /usr/local/etc/postfix/main.cf:
	   smtp_tls_policy_maps = hash:$config_directory/tls_policy
	   # Postfix 2.5 and later
	   smtp_tls_fingerprint_digest = md5

       /usr/local/etc/postfix/tls_policy:
	   example.edu		       none
	   example.mil		       may
	   example.gov		       encrypt protocols=TLSv1
	   example.com		       verify ciphers=high
	   example.net		       secure
	   .example.net		       secure match=.example.net:example.net
	   [mail.example.org]:587      secure match=nexthop
	   # Postfix 2.5 and later
	   [thumb.example.org]		fingerprint
	    match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
	    match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1

       Note:  The  hostname  strategy  if  listed  in a non-default setting of
       smtp_tls_secure_cert_match or in the match attribute in the policy  ta‐
       ble  can	 render the secure level vulnerable to DNS forgery. Do not use
       the hostname strategy for secure-channel configurations in environments
       where DNS security is not assured.

       This feature is available in Postfix 2.3 and later.

smtp_tls_protocols (default: !SSLv2)
       List  of	 TLS  protocols	 that  the Postfix SMTP client will exclude or
       include with opportunistic TLS encryption. Starting with	 Postfix  2.6,
       the Postfix SMTP client will by default not use the obsolete SSLv2 pro‐
       tocol.

       In main.cf the values are separated by whitespace, commas or colons. In
       the policy table (see smtp_tls_policy_maps) the only valid separator is
       colon. An empty value means allow all  protocols.  The  valid  protocol
       names, (see \fBfBSSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1".

       To  include  a  protocol	 list its name, to exclude it, prefix the name
       with a "!" character. To exclude SSLv2 even for opportunistic  TLS  set
       "smtp_tls_protocols  = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
       "smtp_tls_protocols = !SSLv2, !SSLv3". Explicitly listing the protocols
       to  include,  is	 supported,  but  not recommended. OpenSSL provides no
       mechanisms for excluding protocols not known at compile-time. If	 Post‐
       fix  is linked against an OpenSSL library that supports additional pro‐
       tocol versions, they cannot be excluded using either syntax.

       Example:
       # TLSv1 only!
       smtp_tls_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.6 and later.

smtp_tls_scert_verifydepth (default: 9)
       The verification depth for remote SMTP server certificates. A depth  of
       1 is sufficient if the issuing CA is listed in a local CA file.

       The  default verification depth is 9 (the OpenSSL default) for compati‐
       bility with earlier Postfix behavior. Prior to Postfix 2.5, the default
       value  was  5, but the limit was not actually enforced. If you have set
       this to a lower	non-default  value,  certificates  with	 longer	 trust
       chains  may  now fail to verify. Certificate chains with 1 or 2 CAs are
       common, deeper chains are more rare and any  number  between  5	and  9
       should suffice in practice. You can choose a lower number if, for exam‐
       ple, you trust certificates directly signed by an issuing  CA  but  not
       any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtp_tls_secure_cert_match (default: nexthop, dot-nexthop)
       The  server  certificate	 peername verification method for the "secure"
       TLS security level. In a	 "secure"  TLS	policy	table  ($smtp_tls_pol‐
       icy_maps)  entry	 the optional "match" attribute overrides this main.cf
       setting.

       This parameter specifies one or more patterns or	 strategies  separated
       by  commas,  whitespace	or colons.  In the policy table the only valid
       separator is the colon character.

       For  a  description  of	the  pattern  and  strategy  syntax  see   the
       smtp_tls_verify_cert_match parameter. The "hostname" strategy should be
       avoided in this context, as in the absence  of  a  secure  global  DNS,
       using  the  results  of	MX  lookups in certificate verification is not
       immune to active (man-in-the-middle) attacks on DNS.

       Sample main.cf setting:

	   smtp_tls_secure_cert_match = nexthop

       Sample policy table override:

	   example.net	   secure match=example.com:.example.com
	   .example.net	   secure match=example.com:.example.com

       This feature is available in Postfix 2.3 and later.

smtp_tls_security_level (default: empty)
       The default SMTP TLS security level for the Postfix SMTP client; when a
       non-empty  value	 is  specified, this overrides the obsolete parameters
       smtp_use_tls, smtp_enforce_tls, and smtp_tls_enforce_peername.

       Specify one of the following security levels:

       none   TLS will not be used unless enabled  for	specific  destinations
	      via smtp_tls_policy_maps.

       may    Opportunistic  TLS.  Use	TLS if this is supported by the remote
	      SMTP server, otherwise use plaintext. Since sending in the clear
	      is  acceptable,  demanding  stronger  than  default TLS security
	      merely reduces inter-operability.	  The  "smtp_tls_ciphers"  and
	      "smtp_tls_protocols"  (Postfix  >= 2.6) configuration parameters
	      provide control over the protocols and cipher  grade  used  with
	      opportunistic  TLS.  With earlier releases the opportunistic TLS
	      cipher grade is always "export" and no protocols	are  disabled.
	      When  TLS	 handshakes  fail,  the connection is retried with TLS
	      disabled.	 This allows mail delivery to sites with  non-interop‐
	      erable TLS implementations.

       encrypt
	      Mandatory	 TLS  encryption. Since a minimum level of security is
	      intended, it is reasonable to  be	 specific  about  sufficiently
	      secure protocol versions and ciphers. At this security level and
	      higher, the main.cf parameters smtp_tls_mandatory_protocols  and
	      smtp_tls_mandatory_ciphers specify the TLS protocols and minimum
	      cipher grade which the administrator considers secure enough for
	      mandatory	 encrypted  sessions.  This  security  level is not an
	      appropriate default for systems delivering mail to the Internet.

       fingerprint
	      Certificate fingerprint verification. Available with Postfix 2.5
	      and later. At this security level, there are no trusted certifi‐
	      cate authorities. The certificate trust chain, expiration	 date,
	      ...    are    not	  checked.   Instead,	the   smtp_tls_finger‐
	      print_cert_match parameter lists the valid "fingerprints" of the
	      server  certificate.  The digest algorithm used to calculate the
	      fingerprint  is  selected	 by  the   smtp_tls_fingerprint_digest
	      parameter.

       verify Mandatory	 TLS  verification.  At	 this  security	 level, DNS MX
	      lookups are trusted to be secure enough, and the	name  verified
	      in  the  server  certificate  is usually obtained indirectly via
	      unauthenticated DNS MX lookups.  The  smtp_tls_verify_cert_match
	      parameter	 controls how the server name is verified. In practice
	      explicit control over matching is more common  at	 the  "secure"
	      level,  described below. This security level is not an appropri‐
	      ate default for systems delivering mail to the Internet.

       secure Secure-channel TLS.  At this security  level,  DNS  MX  lookups,
	      though  potentially  used	 to  determine	the candidate next-hop
	      gateway IP addresses, are not trusted to be  secure  enough  for
	      TLS peername verification. Instead, the default name verified in
	      the server certificate is obtained from the next-hop  domain  as
	      specified in the smtp_tls_secure_cert_match configuration param‐
	      eter. The default matching rule is  that	a  server  certificate
	      matches when its name is equal to or is a sub-domain of the nex‐
	      thop domain. This security level is not an  appropriate  default
	      for systems delivering mail to the Internet.

       Examples:

       # No TLS. Formerly: smtp_use_tls=no and smtp_enforce_tls=no.
       smtp_tls_security_level = none

       # Opportunistic TLS.
       smtp_tls_security_level = may
       # Postfix >= 2.6:
       # Do not tweak opportunistic ciphers or protocol unless it is essential
       # to do so (if a security vulnerability is found in the SSL library that
       # can be mitigated by disabling a particular protocol or raising the
       # cipher grade from "export" to "low" or "medium").
       smtp_tls_ciphers = export
       smtp_tls_protocols = !SSLv2

       # Mandatory (high-grade) TLS encryption.
       smtp_tls_security_level = encrypt
       smtp_tls_mandatory_ciphers = high

       # Mandatory TLS verification of hostname or nexthop domain.
       smtp_tls_security_level = verify
       smtp_tls_mandatory_ciphers = high
       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       # Secure channel TLS with exact nexthop name match.
       smtp_tls_security_level = secure
       smtp_tls_mandatory_protocols = TLSv1
       smtp_tls_mandatory_ciphers = high
       smtp_tls_secure_cert_match = nexthop

       # Certificate fingerprint verification (Postfix >= 2.5).
       # The CA-less "fingerprint" security level only scales to a limited
       # number of destinations. As a global default rather than a per-site
       # setting, this is practical when mail for all recipients is sent
       # to a central mail hub.
       relayhost = [mailhub.example.com]
       smtp_tls_security_level = fingerprint
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       smtp_tls_mandatory_ciphers = high
       smtp_tls_fingerprint_cert_match =
	   3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
	   EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.3 and later.

smtp_tls_session_cache_database (default: empty)
       Name  of	 the file containing the optional Postfix SMTP client TLS ses‐
       sion cache. Specify a database type that supports enumeration, such  as
       btree or sdbm; there is no need to support concurrent access.  The file
       is created if it does not exist. The smtp(8) daemon does not  use  this
       parameter  directly,  rather the cache is implemented indirectly in the
       tlsmgr(8) daemon. This means that per-smtp-instance master.cf overrides
       of  this	 parameter  are	 not  effective.  Note, that each of the cache
       databases supported by tlsmgr(8) daemon: $smtpd_tls_session_cache_data‐
       base,  $smtp_tls_session_cache_database (and with Postfix 2.3 and later
       $lmtp_tls_session_cache_database), needs to be stored separately. It is
       not  at	this  time possible to store multiple caches in a single data‐
       base.

       Note: dbm databases are not  suitable.  TLS  session  objects  are  too
       large.

       As  of version 2.5, Postfix no longer uses root privileges when opening
       this file. The file  should  now	 be  stored  under  the	 Postfix-owned
       data_directory. As a migration aid, an attempt to open the file under a
       non-Postfix directory is redirected to  the  Postfix-owned  data_direc‐
       tory, and a warning is logged.

       Example:

       smtp_tls_session_cache_database = btree:/var/lib/postfix/smtp_scache

       This feature is available in Postfix 2.2 and later.

smtp_tls_session_cache_timeout (default: 3600s)
       The  expiration	time of Postfix SMTP client TLS session cache informa‐
       tion.  A cache cleanup is performed periodically	 every	$smtp_tls_ses‐
       sion_cache_timeout  seconds.  As with $smtp_tls_session_cache_database,
       this parameter is implemented in the  tlsmgr(8)	daemon	and  therefore
       per-smtp-instance master.cf overrides are not possible.

       This feature is available in Postfix 2.2 and later.

smtp_tls_verify_cert_match (default: hostname)
       The  server  certificate	 peername verification method for the "verify"
       TLS security level. In a	 "verify"  TLS	policy	table  ($smtp_tls_pol‐
       icy_maps)  entry	 the optional "match" attribute overrides this main.cf
       setting.

       This parameter specifies one or more patterns or	 strategies  separated
       by  commas,  whitespace	or colons.  In the policy table the only valid
       separator is the colon character.

       Patterns specify domain names, or domain name suffixes:

       example.com
	      Match the example.com domain, i.e. one of the names  the	server
	      certificate  must	 be example.com, upper and lower case distinc‐
	      tions are ignored.

       .example.com
	      Match subdomains of the example.com domain, i.e. match a name in
	      the  server  certificate	that  consists of a non-zero number of
	      labels followed by a .example.com suffix. Case distinctions  are
	      ignored.

       Strategies  specify  a  transformation  from the next-hop domain to the
       expected name in the server certificate:

       nexthop
	      Match against the next-hop domain, which is either the recipient
	      domain,  or  the	transport  next-hop  configured for the domain
	      stripped of any optional socket type  prefix,  enclosing	square
	      brackets	and trailing port. When MX lookups are not suppressed,
	      this is the original nexthop domain prior to the MX lookup,  not
	      the  result  of the MX lookup. For LMTP delivery via UNIX-domain
	      sockets, the verified next-hop name is $myhostname.  This strat‐
	      egy  is  suitable	 for  use  with	 the  "secure" policy. Case is
	      ignored.

       dot-nexthop
	      As above, but match server certificate names that are subdomains
	      of the next-hop domain. Case is ignored.

       hostname
	      Match  against the hostname of the server, often obtained via an
	      unauthenticated DNS MX lookup. For LMTP delivery via UNIX-domain
	      sockets, the verified name is $myhostname. This matches the ver‐
	      ification	 strategy  of  the  "MUST"  keyword  in	 the  obsolete
	      smtp_tls_per_site	 table, and is suitable for use with the "ver‐
	      ify" security level. When	 the  next-hop	name  is  enclosed  in
	      square  brackets to suppress MX lookups, the "hostname" strategy
	      is the same as the "nexthop" strategy. Case is ignored.

       Sample main.cf setting:

       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       Sample policy table override:

       example.com     verify  match=hostname:nexthop
       .example.com    verify  match=example.com:.example.com:hostname

       This feature is available in Postfix 2.3 and later.

smtp_use_tls (default: no)
       Opportunistic mode: use TLS when a remote SMTP server announces	START‐
       TLS  support,  otherwise	 send the mail in the clear. Beware: some SMTP
       servers offer STARTTLS even if it is not configured.   With  Postfix  <
       2.3,  if	 the  TLS  handshake  fails, and no other server is available,
       delivery is deferred and mail stays in the queue. If this is a  concern
       for you, use the smtp_tls_per_site feature instead.

       This  feature  is  available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtp_tls_security_level instead.

smtp_xforward_timeout (default: 300s)
       The SMTP client time limit for sending the XFORWARD  command,  and  for
       receiving the server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_authorized_verp_clients (default: $authorized_verp_clients)
       What SMTP clients are allowed to specify the XVERP command.  This  com‐
       mand requests that mail be delivered one recipient at a time with a per
       recipient return address.

       By default, no clients are allowed to specify XVERP.

       This parameter was renamed with Postfix version 2.1. The default	 value
       is backwards compatible with Postfix version 2.0.

       Specify	a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the	 network  part
       of a host address. You can also specify hostnames or .domain names (the
       initial	dot  causes  the  domain  to  match  any   name	  below	  it),
       "/file/name"  or	 "type:table"  patterns.   A  "/file/name"  pattern is
       replaced by its contents; a "type:table" lookup table is matched when a
       table  entry  matches  a	 lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace.  Specify
       "!pattern"  to  exclude	an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside	[]  in
       the  smtpd_authorized_verp_clients  value,  and in files specified with
       "/file/name".  IP version 6 addresses contain the  ":"  character,  and
       would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xclient_hosts (default: empty)
       What SMTP clients are allowed to use the XCLIENT feature.  This command
       overrides SMTP client information that is used for access control. Typ‐
       ical use is for SMTP-based content filters, fetchmail-like programs, or
       SMTP server access rule testing. See the	 XCLIENT_README	 document  for
       details.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XCLIENT.

       Specify	a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the	 network  part
       of a host address. You can also specify hostnames or .domain names (the
       initial	dot  causes  the  domain  to  match  any   name	  below	  it),
       "/file/name"  or	 "type:table"  patterns.   A  "/file/name"  pattern is
       replaced by its contents; a "type:table" lookup table is matched when a
       table  entry  matches  a	 lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace.  Specify
       "!pattern"  to  exclude	an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside	[]  in
       the  smtpd_authorized_xclient_hosts  value, and in files specified with
       "/file/name".  IP version 6 addresses contain the  ":"  character,  and
       would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xforward_hosts (default: empty)
       What  SMTP  clients are allowed to use the XFORWARD feature.  This com‐
       mand forwards information that is used to improve logging  after	 SMTP-
       based content filters. See the XFORWARD_README document for details.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XFORWARD.

       Specify	a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the	 network  part
       of a host address. You can also specify hostnames or .domain names (the
       initial	dot  causes  the  domain  to  match  any   name	  below	  it),
       "/file/name"  or	 "type:table"  patterns.   A  "/file/name"  pattern is
       replaced by its contents; a "type:table" lookup table is matched when a
       table  entry  matches  a	 lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace.  Specify
       "!pattern"  to  exclude	an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside	[]  in
       the  smtpd_authorized_xforward_hosts value, and in files specified with
       "/file/name".  IP version 6 addresses contain the  ":"  character,  and
       would otherwise be confused with a "type:table" pattern.

smtpd_banner (default: $myhostname ESMTP $mail_name)
       The  text that follows the 220 status code in the SMTP greeting banner.
       Some people like to see the mail version advertised. By default,	 Post‐
       fix shows no version.

       You MUST specify $myhostname at the start of the text. This is required
       by the SMTP protocol.

       Example:

       smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)

smtpd_client_connection_count_limit (default: 50)
       How many simultaneous connections any client is allowed to make to this
       service.	  By  default,	the  limit  is set to half the default process
       limit value.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not  be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

smtpd_client_connection_rate_limit (default: 0)
       The maximal number of connection attempts any client is allowed to make
       to this service per time unit.  The time unit  is  specified  with  the
       anvil_rate_time_unit configuration parameter.

       By  default,  a	client	can  make as many connections per time unit as
       Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not  be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_connection_rate_limit = 1000

smtpd_client_event_limit_exceptions (default: $mynetworks)
       Clients that are excluded from smtpd_client_*_count/rate_limit restric‐
       tions. See the mynetworks parameter description for the parameter value
       syntax.

       By default, clients in trusted networks are excluded. Specify a list of
       network blocks, hostnames or .domain names (the initial dot causes  the
       domain to match any name below it).

       Note:  IP  version 6 address information must be specified inside [] in
       the smtpd_client_event_limit_exceptions value, and in  files  specified
       with  "/file/name".   IP version 6 addresses contain the ":" character,
       and would otherwise be confused with a "type:table" pattern.

       This feature is available in Postfix 2.2 and later.

smtpd_client_message_rate_limit (default: 0)
       The maximal number of message delivery  requests	 that  any  client  is
       allowed to make to this service per time unit, regardless of whether or
       not Postfix actually accepts those messages.  The time unit  is	speci‐
       fied with the anvil_rate_time_unit configuration parameter.

       By  default,  a	client	can send as many message delivery requests per
       time unit as Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not  be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_message_rate_limit = 1000

smtpd_client_new_tls_session_rate_limit (default: 0)
       The  maximal  number of new (i.e., uncached) TLS sessions that a remote
       SMTP client is allowed to negotiate with this service  per  time	 unit.
       The  time unit is specified with the anvil_rate_time_unit configuration
       parameter.

       By default, a remote SMTP client can negotiate as many new TLS sessions
       per time unit as Postfix can accept.

       To  disable  this  feature,  specify a limit of 0. Otherwise, specify a
       limit that is at least the per-client concurrent session limit, or else
       legitimate client sessions may be rejected.

       WARNING:	 The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.3 and later.

       Example:

       smtpd_client_new_tls_session_rate_limit = 100

smtpd_client_port_logging (default: no)
       Enable logging of the remote SMTP client port in addition to the	 host‐
       name and IP address. The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

smtpd_client_recipient_rate_limit (default: 0)
       The maximal number of recipient addresses that any client is allowed to
       send to this service per time unit, regardless of whether or not	 Post‐
       fix actually accepts those recipients.  The time unit is specified with
       the anvil_rate_time_unit configuration parameter.

       By default, a client can send as many recipient addresses per time unit
       as Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING:	 The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_recipient_rate_limit = 1000

smtpd_client_restrictions (default: empty)
       Optional SMTP server access restrictions in the	context	 of  a	client
       SMTP  connection	 request.   See	 SMTPD_ACCESS_README, section "Delayed
       evaluation of SMTP access restriction lists" for a discussion of evalu‐
       ation context and time.

       The default is to allow all connection requests.

       Specify	a list of restrictions, separated by commas and/or whitespace.
       Continue	 long  lines  by  starting  the	 next  line  with  whitespace.
       Restrictions  are applied in the order as specified; the first restric‐
       tion that matches wins.

       The following restrictions are specific to client  hostname  or	client
       network address information.

       check_ccert_access type:table
	      Use  the	client	certificate  fingerprint as lookup key for the
	      specified access(5) database; with  Postfix  version  2.2,  also
	      require  that  the  SMTP client certificate is verified success‐
	      fully.  The fingerprint digest algorithm is configurable via the
	      smtpd_tls_fingerprint_digest  parameter (hard-coded as md5 prior
	      to Postfix version 2.5).	This feature is available with Postfix
	      version 2.2 and later.

       check_client_access type:table
	      Search  the  specified  access database for the client hostname,
	      parent domains, client  IP  address,  or	networks  obtained  by
	      stripping	 least	significant  octets.  See the access(5) manual
	      page for details.

       check_client_mx_access type:table
	      Search the specified access(5) database for the MX hosts for the
	      client  hostname, and execute the corresponding action.  Note: a
	      result of "OK" is not allowed for safety reasons.	 Instead,  use
	      DUNNO  in order to exclude specific hosts from blacklists.  This
	      feature is available in Postfix 2.7 and later.

       check_client_ns_access type:table
	      Search the specified access(5) database for the DNS servers  for
	      the  client  hostname,  and  execute  the	 corresponding action.
	      Note: a result of	 "OK"  is  not	allowed	 for  safety  reasons.
	      Instead,	use  DUNNO  in	order  to  exclude specific hosts from
	      blacklists.  This feature is available in Postfix 2.7 and later.

       check_reverse_client_hostname_access type:table
	      Search the specified access database for the unverified  reverse
	      client  hostname, parent domains, client IP address, or networks
	      obtained	by  stripping  least  significant  octets.   See   the
	      access(5)	 manual	 page  for details.  Note: a result of "OK" is
	      not allowed for safety reasons.  Instead, use DUNNO in order  to
	      exclude  specific hosts from blacklists.	This feature is avail‐
	      able in Postfix 2.6 and later.

       check_reverse_client_hostname_mx_access type:table
	      Search the specified access(5) database for the MX hosts for the
	      unverified  reverse client hostname, and execute the correspond‐
	      ing action.  Note: a result of "OK" is not  allowed  for	safety
	      reasons.	 Instead, use DUNNO in order to exclude specific hosts
	      from blacklists.	This feature is available in Postfix  2.7  and
	      later.

       check_reverse_client_hostname_ns_access type:table
	      Search  the specified access(5) database for the DNS servers for
	      the unverified reverse client hostname, and execute  the	corre‐
	      sponding	action.	  Note:	 a  result  of "OK" is not allowed for
	      safety reasons.  Instead, use DUNNO in order to exclude specific
	      hosts from blacklists.  This feature is available in Postfix 2.7
	      and later.

       permit_inet_interfaces
	      Permit  the  request  when  the  client	IP   address   matches
	      $inet_interfaces.

       permit_mynetworks
	      Permit  the  request when the client IP address matches any net‐
	      work or network address listed in	 $mynetworks.

       permit_sasl_authenticated
	      Permit the request when the client is successfully authenticated
	      via the RFC 4954 (AUTH) protocol.

       permit_tls_all_clientcerts
	      Permit  the  request  when the remote SMTP client certificate is
	      verified successfully.  This option must be used only if a  spe‐
	      cial  CA	issues	the certificates and only this CA is listed as
	      trusted CA. Otherwise, clients with  a  third-party  certificate
	      would  also be allowed to relay.	Specify "tls_append_default_CA
	      = no" when the trusted CA is specified with smtpd_tls_CAfile  or
	      smtpd_tls_CApath,	 to prevent Postfix from appending the system-
	      supplied default CAs.  This feature is  available	 with  Postfix
	      version 2.2.

       permit_tls_clientcerts
	      Permit  the request when the remote SMTP client certificate fin‐
	      gerprint	is  listed  in	$relay_clientcerts.   The  fingerprint
	      digest  algorithm	 is  configurable  via	the  smtpd_tls_finger‐
	      print_digest parameter (hard-coded as md5 prior to Postfix  ver‐
	      sion 2.5).  This feature is available with Postfix version 2.2.

       reject_rbl_client rbl_domain=d.d.d.d
	      Reject  the  request when the reversed client network address is
	      listed with the A record	"d.d.d.d"  under  rbl_domain  (Postfix
	      version  2.1  and	 later	only).	If no "=d.d.d.d" is specified,
	      reject the request when the reversed client network  address  is
	      listed with any A record under rbl_domain.
	      The  maps_rbl_reject_code	 parameter specifies the response code
	      for rejected requests  (default:	 554),	the  default_rbl_reply
	      parameter	  specifies   the   default   server  reply,  and  the
	      rbl_reply_maps  parameter specifies tables with  server  replies
	      indexed by rbl_domain.  This feature is available in Postfix 2.0
	      and later.

       permit_dnswl_client dnswl_domain=d.d.d.d
	      Accept the request when the reversed client network  address  is
	      listed  with  the	 A record "d.d.d.d" under dnswl_domain.	 If no
	      "=d.d.d.d" is specified, accept the request  when	 the  reversed
	      client  network  address	is  listed  with  any  A  record under
	      dnswl_domain.
	      For safety, permit_dnswl_client  is  silently  ignored  when  it
	      would   override	 reject_unauth_destination.    The  result  is
	      DEFER_IF_REJECT when whitelist lookup fails.   This  feature  is
	      available in Postfix 2.8 and later.

       reject_rhsbl_client rbl_domain=d.d.d.d
	      Reject the request when the client hostname is listed with the A
	      record "d.d.d.d" under rbl_domain (Postfix version 2.1 and later
	      only).   If  no "=d.d.d.d" is specified, reject the request when
	      the  client  hostname  is	 listed	 with  any  A	record	 under
	      rbl_domain.  See	the  reject_rbl_client	description  above for
	      additional RBL related configuration parameters.	 This  feature
	      is  available in Postfix 2.0 and later; with Postfix version 2.8
	      and later, reject_rhsbl_reverse_client will usually produce bet‐
	      ter results.

       permit_rhswl_client rhswl_domain=d.d.d.d
	      Accept the request when the client hostname is listed with the A
	      record "d.d.d.d" under rhswl_domain.  If no "=d.d.d.d" is speci‐
	      fied, accept the request when the client hostname is listed with
	      any A record under rhswl_domain.
	      Caution: client name whitelisting is fragile, since  the	client
	      name  lookup  can	 fail  due  to temporary outages.  Client name
	      whitelisting should be used only to reduce  false	 positives  in
	      e.g.   DNS-based	blocklists,  and  not  for  making access rule
	      exceptions.
	      For safety, permit_rhswl_client  is  silently  ignored  when  it
	      would   override	 reject_unauth_destination.    The  result  is
	      DEFER_IF_REJECT when whitelist lookup fails.   This  feature  is
	      available in Postfix 2.8 and later.

       reject_rhsbl_reverse_client rbl_domain=d.d.d.d
	      Reject  the  request when the unverified reverse client hostname
	      is listed with the A record "d.d.d.d" under rbl_domain.	If  no
	      "=d.d.d.d"  is specified, reject the request when the unverified
	      reverse client hostname  is  listed  with	 any  A	 record	 under
	      rbl_domain.  See	the  reject_rbl_client	description  above for
	      additional RBL related configuration parameters.	 This  feature
	      is available in Postfix 2.8 and later.

       reject_unknown_client_hostname	   (with      Postfix	   <	  2.3:
       reject_unknown_client)
	      Reject the request when 1) the client IP	address->name  mapping
	      fails,   2)   the	  name->address	  mapping  fails,  or  3)  the
	      name->address mapping does not match the client IP address.
	      This     is     a	    stronger	 restriction	 than	   the
	      reject_unknown_reverse_client_hostname  feature,	which triggers
	      only under condition 1) above.
	      The unknown_client_reject_code parameter specifies the  response
	      code  for	 rejected requests (default: 450). The reply is always
	      450 in case the address->name or name->address lookup failed due
	      to a temporary problem.

       reject_unknown_reverse_client_hostname
	      Reject   the   request   when  the  client  IP  address  has  no
	      address->name mapping.
	      This     is     a	    weaker	restriction	 than	   the
	      reject_unknown_client_hostname  feature, which requires not only
	      that the address->name and  name->address	 mappings  exist,  but
	      also that the two mappings reproduce the client IP address.
	      The  unknown_client_reject_code parameter specifies the response
	      code for rejected requests (default: 450).  The reply is	always
	      450  in  case the address->name lookup failed due to a temporary
	      problem.
	      This feature is available in Postfix 2.3 and later.

       In addition, you can use any of	the  following	generic	 restrictions.
       These restrictions are applicable in any SMTP command context.

       check_policy_service servername
	      Query  the  specified policy server. See the SMTPD_POLICY_README
	      document for details. This feature is available in  Postfix  2.1
	      and later.

       defer  Defer  the  request. The client is told to try again later. This
	      restriction is useful at the end of a restriction list, to  make
	      the default policy explicit.
	      The  defer_code  parameter  specifies the SMTP server reply code
	      (default: 450).

       defer_if_permit
	      Defer the request if some later restriction would result	in  an
	      explicit	or  implicit  PERMIT  action.	This  is useful when a
	      blacklisting feature fails due to	 a  temporary  problem.	  This
	      feature is available in Postfix version 2.1 and later.

       defer_if_reject
	      Defer  the  request  if some later restriction would result in a
	      REJECT action.  This is useful when a whitelisting feature fails
	      due  to a temporary problem.  This feature is available in Post‐
	      fix version 2.1 and later.

       permit Permit the request. This restriction is useful at the end	 of  a
	      restriction list, to make the default policy explicit.

       reject_multi_recipient_bounce
	      Reject the request when the envelope sender is the null address,
	      and the message has multiple envelope recipients. This usage has
	      rare  but	 legitimate  applications:  under  certain conditions,
	      multi-recipient  mail  that  was	posted	with  the  DSN	option
	      NOTIFY=NEVER may be forwarded with the null sender address.
	      Note:  this  restriction	can  only  work	 reliably when used in
	      smtpd_data_restrictions	 or    smtpd_end_of_data_restrictions,
	      because  the  total number of recipients is not known at an ear‐
	      lier stage of the SMTP conversation.  Use at the RCPT stage will
	      only reject the second etc.  recipient.
	      The  multi_recipient_bounce_reject_code  parameter specifies the
	      response code for rejected requests (default:  550).  This  fea‐
	      ture is available in Postfix 2.1 and later.

       reject_plaintext_session
	      Reject  the  request  when the connection is not encrypted. This
	      restriction should not be used  before  the  client  has	had  a
	      chance  to  negotiate  encryption with the AUTH or STARTTLS com‐
	      mands.
	      The plaintext_reject_code parameter specifies the response  code
	      for  rejected  requests (default:	 450).	This feature is avail‐
	      able in Postfix 2.3 and later.

       reject_unauth_pipelining
	      Reject the request when the client sends SMTP commands ahead  of
	      time where it is not allowed, or when the client sends SMTP com‐
	      mands ahead of time without knowing that Postfix	actually  sup‐
	      ports  ESMTP  command pipelining. This stops mail from bulk mail
	      software that improperly uses ESMTP command pipelining in	 order
	      to speed up deliveries.
	      With  Postfix  2.6 and later, the SMTP server sets a per-session
	      flag whenever it detects illegal pipelining, including pipelined
	      EHLO or HELO commands. The reject_unauth_pipelining feature sim‐
	      ply tests whether the flag was set at any point in  time	during
	      the session.
	      With older Postfix versions, reject_unauth_pipelining checks the
	      current status of the input read queue, and  its	usage  is  not
	      recommended in contexts other than smtpd_data_restrictions.

       reject Reject  the  request. This restriction is useful at the end of a
	      restriction list, to make	 the  default  policy  explicit.   The
	      reject_code  configuration parameter specifies the response code
	      for rejected requests (default: 554).

       sleep seconds
	      Pause for the specified number of seconds and proceed  with  the
	      next  restriction in the list, if any. This may stop zombie mail
	      when used as:
	      /usr/local/etc/postfix/main.cf:
		  smtpd_client_restrictions =
		      sleep 1, reject_unauth_pipelining
		  smtpd_delay_reject = no
	      This feature is available in Postfix 2.3.

       warn_if_reject
	      Change the meaning of the next restriction, so that  it  logs  a
	      warning instead of rejecting a request (look for logfile records
	      that contain "reject_warning"). This is useful for  testing  new
	      restrictions in a "live" environment without risking unnecessary
	      loss of mail.

       Other restrictions that are valid in this context:

       ·      SMTP command specific restrictions that are described under  the
	      smtpd_helo_restrictions,	     smtpd_sender_restrictions	    or
	      smtpd_recipient_restrictions parameters. When  helo,  sender  or
	      recipient	 restrictions  are  listed under smtpd_client_restric‐
	      tions, they have effect only with "smtpd_delay_reject = yes", so
	      that  $smtpd_client_restrictions is evaluated at the time of the
	      RCPT TO command.

       Example:

       smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname

smtpd_command_filter (default: empty)
       A mechanism to transform commands from remote SMTP clients.  This is  a
       last-resort  tool to work around client commands that break inter-oper‐
       ability with the Postfix SMTP server.  Other uses involve fault	injec‐
       tion to test Postfix's handling of invalid commands.

       Specify	the  name of a "type:table" lookup table. The search string is
       the SMTP command as received from the remote SMTP client,  except  that
       initial	whitespace  and the trailing <CR><LF> are removed.  The result
       value is executed by the Postfix SMTP server.

       There is no need to use smtpd_command_filter for the following cases:

       ·      Use "resolve_numeric_domain = yes" to accept "user@ipaddress".

       ·      Postfix already accepts the correct form "user@[ipaddress]". Use
	      virtual_alias_maps  or  canonical_maps  to  translate these into
	      domain names if necessary.

       ·      Use "strict_rfc821_envelopes = no" to accept "RCPT TO:<User Name
	      <user@example.com>>".  Postfix  will ignore the "User Name" part
	      and deliver to the <user@example.com> address.

       Examples of problems that can be solved with  the  smtpd_command_filter
       feature:

       /usr/local/etc/postfix/main.cf:
	   smtpd_command_filter = pcre:$config_directory/command_filter

       /usr/local/etc/postfix/command_filter:
	   # Work around clients that send malformed HELO commands.
	   /^HELO\s*$/ HELO domain.invalid

	   # Work around clients that send empty lines.
	   /^\s*$/     NOOP

	   # Work around clients that send RCPT TO:<'user@domain'>.
	   # WARNING: do not lose the parameters that follow the address.
	   /^RCPT\s+TO:\s*<'([^[:space:]]+)'>(.*)/     RCPT TO:<$1>$2

	   # Bounce-never mail sink. Use notify_classes=bounce,resource,software
	   # to send bounced mail to the postmaster (with message body removed).
	   /^(RCPT\s+TO:.*?)\bNOTIFY=\S+\b(.*)/ $1 NOTIFY=NEVER $2
	   /^(RCPT\s+TO:.*)/			$1 NOTIFY=NEVER

       This feature is available in Postfix 2.7.

smtpd_data_restrictions (default: empty)
       Optional	 access	 restrictions  that the Postfix SMTP server applies in
       the context of the SMTP DATA command.  See SMTPD_ACCESS_README, section
       "Delayed	 evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       This feature is available in Postfix 2.0 and later.

       Specify a list of restrictions, separated by commas and/or  whitespace.
       Continue	 long  lines  by  starting  the	 next  line  with  whitespace.
       Restrictions are applied in the order as specified; the first  restric‐
       tion that matches wins.

       The following restrictions are valid in this context:

       ·      Generic  restrictions  that can be used in any SMTP command con‐
	      text, described under smtpd_client_restrictions.

       ·      SMTP   command	specific    restrictions    described	 under
	      smtpd_client_restrictions,	      smtpd_helo_restrictions,
	      smtpd_sender_restrictions or smtpd_recipient_restrictions.

       ·      However, no recipient information is available in	 the  case  of
	      multi-recipient mail. Acting on only one recipient would be mis‐
	      leading,	because	 any  decision	will  affect  all   recipients
	      equally.	Acting on all recipients would require a possibly very
	      large amount of memory, and would also  be  misleading  for  the
	      reasons mentioned before.

       Examples:

       smtpd_data_restrictions = reject_unauth_pipelining
       smtpd_data_restrictions = reject_multi_recipient_bounce

smtpd_delay_open_until_valid_rcpt (default: yes)
       Postpone	 the  start  of an SMTP mail transaction until a valid RCPT TO
       command is received. Specify "no" to create a mail transaction as  soon
       as the SMTP server receives a valid MAIL FROM command.

       With  sites  that  reject lots of mail, the default setting reduces the
       use of disk, CPU and memory resources. The downside  is	that  rejected
       recipients  are	logged	with NOQUEUE instead of a mail transaction ID.
       This complicates the logfile analysis of multi-recipient mail.

       This feature is available in Postfix 2.3 and later.

smtpd_delay_reject (default: yes)
       Wait until the RCPT TO command before evaluating $smtpd_client_restric‐
       tions, $smtpd_helo_restrictions and $smtpd_sender_restrictions, or wait
       until the ETRN command before evaluating $smtpd_client_restrictions and
       $smtpd_helo_restrictions.

       This  feature  is  turned on by default because some clients apparently
       mis-behave when the Postfix SMTP server rejects	commands  before  RCPT
       TO.

       The  default  setting  has  one major benefit: it allows Postfix to log
       recipient address information when rejecting a client  name/address  or
       sender  address, so that it is possible to find out whose mail is being
       rejected.

smtpd_discard_ehlo_keyword_address_maps (default: empty)
       Lookup tables, indexed by the remote SMTP  client  address,  with  case
       insensitive  lists  of EHLO keywords (pipelining, starttls, auth, etc.)
       that the SMTP server will not send in the EHLO  response	 to  a	remote
       SMTP client. See smtpd_discard_ehlo_keywords for details.  The table is
       not searched by hostname for robustness reasons.

       This feature is available in Postfix 2.2 and later.

smtpd_discard_ehlo_keywords (default: empty)
       A case insensitive list of EHLO keywords (pipelining,  starttls,	 auth,
       etc.)  that  the	 SMTP  server  will not send in the EHLO response to a
       remote SMTP client.

       This feature is available in Postfix 2.2 and later.

       Notes:

       ·      Specify the silent-discard pseudo keyword to prevent this action
	      from being logged.

       ·      Use  the smtpd_discard_ehlo_keyword_address_maps feature to dis‐
	      card EHLO keywords selectively.

smtpd_end_of_data_restrictions (default: empty)
       Optional access restrictions that the Postfix SMTP  server  applies  in
       the  context of the SMTP END-OF-DATA command.  See SMTPD_ACCESS_README,
       section "Delayed evaluation of SMTP access  restriction	lists"	for  a
       discussion of evaluation context and time.

       This feature is available in Postfix 2.2 and later.

       See smtpd_data_restrictions for details and limitations.

smtpd_enforce_tls (default: no)
       Mandatory  TLS:	announce STARTTLS support to SMTP clients, and require
       that clients use TLS encryption.	 According to RFC 2487 this  MUST  NOT
       be  applied  in case of a publicly-referenced SMTP server.  This option
       is off by default and should be used only on dedicated servers.

       Note 1: "smtpd_enforce_tls = yes" implies "smtpd_tls_auth_only = yes".

       Note 2: when invoked via	 "sendmail  -bs",  Postfix  will  never	 offer
       STARTTLS	 due  to  insufficient privileges to access the server private
       key. This is intended behavior.

       This feature is available in Postfix 2.2 and later.  With  Postfix  2.3
       and later use smtpd_tls_security_level instead.

smtpd_error_sleep_time (default: 1s)
       With  Postfix  version  2.1  and	 later: the SMTP server response delay
       after a client has made more than $smtpd_soft_error_limit  errors,  and
       fewer than $smtpd_hard_error_limit errors, without delivering mail.

       With  Postfix  version  2.0  and	 earlier: the SMTP server delay before
       sending a reject (4xx or 5xx) response, when the client has made	 fewer
       than $smtpd_soft_error_limit errors without delivering mail.

smtpd_etrn_restrictions (default: empty)
       Optional	 SMTP  server  access  restrictions in the context of a client
       ETRN request.  See SMTPD_ACCESS_README, section "Delayed evaluation  of
       SMTP  access  restriction lists" for a discussion of evaluation context
       and time.

       The Postfix ETRN implementation accepts only destinations that are eli‐
       gible  for  the	Postfix "fast flush" service. See the ETRN_README file
       for details.

       Specify a list of restrictions, separated by commas and/or  whitespace.
       Continue	 long  lines  by  starting  the	 next  line  with  whitespace.
       Restrictions are applied in the order as specified; the first  restric‐
       tion that matches wins.

       The  following restrictions are specific to the domain name information
       received with the ETRN command.

       check_etrn_access type:table
	      Search the specified access database for the ETRN domain name or
	      its parent domains. See the access(5) manual page for details.

       Other restrictions that are valid in this context:

       ·      Generic  restrictions  that can be used in any SMTP command con‐
	      text, described under smtpd_client_restrictions.

       ·      SMTP   command	specific    restrictions    described	 under
	      smtpd_client_restrictions and smtpd_helo_restrictions.

       Example:

       smtpd_etrn_restrictions = permit_mynetworks, reject

smtpd_expansion_filter (default: see postconf -d output)
       What characters are allowed in $name expansions of RBL reply templates.
       Characters not in the allowed set are replaced  by  "_".	  Use  C  like
       escapes to specify special characters such as whitespace.

       This parameter is not subjected to $parameter expansion.

       This feature is available in Postfix 2.0 and later.

smtpd_forbidden_commands (default: CONNECT, GET, POST)
       List of commands that cause the Postfix SMTP server to immediately ter‐
       minate the session with a 221 code. This	 can  be  used	to  disconnect
       clients	that obviously attempt to abuse the system. In addition to the
       commands listed in this parameter, commands that	 follow	 the  "Label:"
       format of message headers will also cause a disconnect.

       This feature is available in Postfix 2.2 and later.

smtpd_hard_error_limit (default: normal: 20, overload: 1)
       The  maximal  number  of errors a remote SMTP client is allowed to make
       without delivering mail. The Postfix SMTP server disconnects  when  the
       limit  is  exceeded.  Normally  the default limit is 20, but it changes
       under overload to just 1. With Postfix 2.5 and earlier, the SMTP server
       always allows up to 20 errors by default.

smtpd_helo_required (default: no)
       Require	that  a	 remote SMTP client introduces itself with the HELO or
       EHLO command before sending the MAIL command  or	 other	commands  that
       require EHLO negotiation.

       Example:

       smtpd_helo_required = yes

smtpd_helo_restrictions (default: empty)
       Optional	 restrictions that the Postfix SMTP server applies in the con‐
       text of	the  SMTP  HELO	 command.   See	 SMTPD_ACCESS_README,  section
       "Delayed	 evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       The default is to permit everything.

       Specify a list of restrictions, separated by commas and/or  whitespace.
       Continue	 long  lines  by  starting  the	 next  line  with  whitespace.
       Restrictions are applied in the order as specified; the first  restric‐
       tion that matches wins.

       The  following  restrictions  are  specific to the hostname information
       received with the HELO or EHLO command.

       check_helo_access type:table
	      Search the specified access(5) database for  the	HELO  or  EHLO
	      hostname	or  parent  domains,  and  execute  the	 corresponding
	      action.

       check_helo_mx_access type:table
	      Search the specified access(5) database for the MX hosts for the
	      HELO  or	EHLO  hostname,	 and execute the corresponding action.
	      Note: a result of	 "OK"  is  not	allowed	 for  safety  reasons.
	      Instead,	use  DUNNO  in	order  to  exclude specific hosts from
	      blacklists.  This feature is available in Postfix 2.1 and later.

       check_helo_ns_access type:table
	      Search the specified access(5) database for the DNS servers  for
	      the HELO or EHLO hostname, and execute the corresponding action.
	      Note: a result of	 "OK"  is  not	allowed	 for  safety  reasons.
	      Instead,	use  DUNNO  in	order  to  exclude specific hosts from
	      blacklists.  This feature is available in Postfix 2.1 and later.

       reject_invalid_helo_hostname (with Postfix < 2.3:  reject_invalid_host‐
       name)
	      Reject  the  request  when  the  HELO or EHLO hostname syntax is
	      invalid.
	      The invalid_hostname_reject_code specifies the response code for
	      rejected requests (default: 501).

       reject_non_fqdn_helo_hostname	   (with      Postfix	   <	  2.3:
       reject_non_fqdn_hostname)
	      Reject the request when the HELO or  EHLO	 hostname  is  not  in
	      fully-qualified domain form, as required by the RFC.
	      The  non_fqdn_reject_code	 parameter specifies the response code
	      for rejected requests (default: 504).

       reject_rhsbl_helo rbl_domain=d.d.d.d
	      Reject the request when the HELO or EHLO	hostname  hostname  is
	      listed  with  the	 A  record "d.d.d.d" under rbl_domain (Postfix
	      version 2.1 and later only).  If	no  "=d.d.d.d"	is  specified,
	      reject the request when the HELO or EHLO hostname is listed with
	      any  A  record  under  rbl_domain.  See  the   reject_rbl_client
	      description for additional RBL related configuration parameters.
	      This feature is available in Postfix 2.0 and later.

       reject_unknown_helo_hostname (with Postfix < 2.3:  reject_unknown_host‐
       name)
	      Reject  the  request when the HELO or EHLO hostname has no DNS A
	      or MX record.
	      The unknown_hostname_reject_code parameter specifies the numeri‐
	      cal response code for rejected requests (default: 450).
	      The  unknown_helo_hostname_tempfail_action  parameter  specifies
	      the action after a temporary DNS error  (default:	 defer_if_per‐
	      mit).

       Other restrictions that are valid in this context:

       ·      Generic  restrictions  that can be used in any SMTP command con‐
	      text, described under smtpd_client_restrictions.

       ·      Client  hostname	or  network  address   specific	  restrictions
	      described under smtpd_client_restrictions.

       ·      SMTP    command	 specific    restrictions    described	 under
	      smtpd_sender_restrictions or smtpd_recipient_restrictions.  When
	      sender	or    recipient	   restrictions	  are	listed	 under
	      smtpd_helo_restrictions,	 they	have	effect	  only	  with
	      "smtpd_delay_reject  = yes", so that $smtpd_helo_restrictions is
	      evaluated at the time of the RCPT TO command.

       Examples:

       smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname
       smtpd_helo_restrictions = permit_mynetworks, reject_unknown_helo_hostname

smtpd_history_flush_threshold (default: 100)
       The maximal number of lines in the Postfix SMTP server command  history
       before it is flushed upon receipt of EHLO, RSET, or end of DATA.

smtpd_junk_command_limit (default: normal: 100, overload: 1)
       The  number  of	junk commands (NOOP, VRFY, ETRN or RSET) that a remote
       SMTP client can send before the Postfix SMTP server starts to increment
       the  error  counter  with each junk command.  The junk command count is
       reset after mail is delivered.  See also the smtpd_error_sleep_time and
       smtpd_soft_error_limit  configuration parameters.  Normally the default
       limit is 100, but it changes under overload to just 1. With Postfix 2.5
       and  earlier,  the SMTP server always allows up to 100 junk commands by
       default.

smtpd_milters (default: empty)
       A list of Milter (mail filter) applications for new mail	 that  arrives
       via  the	 Postfix  smtpd(8) server.  See the MILTER_README document for
       details.

       This feature is available in Postfix 2.3 and later.

smtpd_noop_commands (default: empty)
       List of commands that the Postfix SMTP server replies to with "250 Ok",
       without	doing any syntax checks and without changing state.  This list
       overrides any commands built into the Postfix SMTP server.

smtpd_null_access_lookup_key (default: <;>)
       The lookup key to be used in SMTP access(5) tables instead of the  null
       sender address.

smtpd_peername_lookup (default: yes)
       Attempt to look up the remote SMTP client hostname, and verify that the
       name matches the client IP address. A client name is set	 to  "unknown"
       when  it	 cannot	 be looked up or verified, or when name lookup is dis‐
       abled.  Turning off name lookup reduces delays due to  DNS  lookup  and
       increases the maximal inbound delivery rate.

       This feature is available in Postfix 2.3 and later.

smtpd_policy_service_max_idle (default: 300s)
       The time after which an idle SMTPD policy service connection is closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_max_ttl (default: 1000s)
       The  time  after	 which	an  active  SMTPD policy service connection is
       closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_timeout (default: 100s)
       The time limit for connecting to, writing to or receiving from a	 dele‐
       gated SMTPD policy server.

       This feature is available in Postfix 2.1 and later.

smtpd_proxy_ehlo (default: $myhostname)
       How  the	 Postfix SMTP server announces itself to the proxy filter.  By
       default, the Postfix hostname is used.

       This feature is available in Postfix 2.1 and later.

smtpd_proxy_filter (default: empty)
       The hostname and TCP port of the	 mail  filtering  proxy	 server.   The
       proxy  receives	all mail from the Postfix SMTP server, and is supposed
       to give the result to another Postfix SMTP server process.

       Specify	"host:port"  or	 "inet:host:port"  for	a  TCP	endpoint,   or
       "unix:pathname"	for  a UNIX-domain endpoint. The host can be specified
       as an IP address or as a symbolic name; no MX lookups are  done.	  When
       no  "host"  or  "host:"	 are  specified, the local machine is assumed.
       Pathname interpretation is relative to the Postfix queue directory.

       This feature is available in Postfix 2.1 and later.

       The "inet:" and "unix:" prefixes	 are  available	 in  Postfix  2.3  and
       later.

smtpd_proxy_options (default: empty)
       List  of	 options that control how the Postfix SMTP server communicates
       with a before-queue content filter. Specify zero or more of the follow‐
       ing, separated by comma or whitespace.

       speed_adjust
	      Do  not connect to a before-queue content filter until an entire
	      message has been received. This reduces the number of simultane‐
	      ous before-queue content filter processes.

       NOTE  1:	 A  filter  must not selectively reject recipients of a multi-
       recipient message.  Rejecting all recipients is OK, as is accepting all
       recipients.

       NOTE  2:	 This feature increases the minimum amount of free queue space
       by $message_size_limit. The extra space is needed to save  the  message
       to a temporary file.

       This feature is available in Postfix 2.7 and later.

smtpd_proxy_timeout (default: 100s)
       The  time  limit	 for  connecting  to a proxy filter and for sending or
       receiving information.  When a  connection  fails  the  client  gets  a
       generic	error message while more detailed information is logged to the
       maillog file.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_recipient_limit (default: 1000)
       The  maximal  number of recipients that the Postfix SMTP server accepts
       per message delivery request.

smtpd_recipient_overshoot_limit (default: 1000)
       The number of recipients that a remote SMTP client can send  in	excess
       of  the limit specified with $smtpd_recipient_limit, before the Postfix
       SMTP server increments the per-session  error  count  for  each	excess
       recipient.

smtpd_recipient_restrictions (default: permit_mynetworks, reject_unauth_desti‐
       nation)
       The access restrictions that the Postfix SMTP  server  applies  in  the
       context	of  the	 RCPT  TO  command.   See SMTPD_ACCESS_README, section
       "Delayed evaluation of SMTP access restriction lists" for a  discussion
       of evaluation context and time.

       By default, the Postfix SMTP server accepts:

       ·      Mail from clients whose IP address matches $mynetworks, or:

       ·      Mail  to	remote	destinations that match $relay_domains, except
	      for addresses that contain sender-specified routing  (user@else‐
	      where@domain), or:

       ·      Mail  to	local  destinations  that  match  $inet_interfaces  or
	      $proxy_interfaces,  $mydestination,  $virtual_alias_domains,  or
	      $virtual_mailbox_domains.

       IMPORTANT:  If  you  change this parameter setting, you must specify at
       least one of the following restrictions. Otherwise Postfix will	refuse
       to receive mail:

	   reject, defer, defer_if_permit, reject_unauth_destination

       Specify	a list of restrictions, separated by commas and/or whitespace.
       Continue	 long  lines  by  starting  the	 next  line  with  whitespace.
       Restrictions  are applied in the order as specified; the first restric‐
       tion that matches wins.

       The following restrictions are specific to the recipient	 address  that
       is received with the RCPT TO command.

       check_recipient_access type:table
	      Search the specified access(5) database for the resolved RCPT TO
	      address, domain, parent domains, or localpart@, and execute  the
	      corresponding action.

       check_recipient_mx_access type:table
	      Search the specified access(5) database for the MX hosts for the
	      RCPT TO domain, and execute the corresponding action.   Note:  a
	      result  of  "OK" is not allowed for safety reasons. Instead, use
	      DUNNO in order to exclude specific hosts from blacklists.	  This
	      feature is available in Postfix 2.1 and later.

       check_recipient_ns_access type:table
	      Search  the specified access(5) database for the DNS servers for
	      the RCPT TO domain, and execute the corresponding action.	 Note:
	      a result of "OK" is not allowed for safety reasons. Instead, use
	      DUNNO in order to exclude specific hosts from blacklists.	  This
	      feature is available in Postfix 2.1 and later.

       permit_auth_destination
	      Permit the request when one of the following is true:

       ·      Postfix  is  mail forwarder: the resolved RCPT TO domain matches
	      $relay_domains or a subdomain thereof, and the address  contains
	      no sender-specified routing (user@elsewhere@domain),

       ·      Postfix  is  the	final destination: the resolved RCPT TO domain
	      matches  $mydestination,	$inet_interfaces,   $proxy_interfaces,
	      $virtual_alias_domains,  or  $virtual_mailbox_domains,  and  the
	      address  contains	 no   sender-specified	 routing   (user@else‐
	      where@domain).

       permit_mx_backup
	      Permit  the  request when the local mail system is backup MX for
	      the RCPT TO domain, or when the domain is an authorized destina‐
	      tion (see permit_auth_destination for definition).

       ·      Safety:  permit_mx_backup	 does  not  accept addresses that have
	      sender-specified	routing	  information	(example:   user@else‐
	      where@domain).

       ·      Safety:  permit_mx_backup	 can  be  vulnerable  to  mis-use when
	      access is not restricted with permit_mx_backup_networks.

       ·      Safety: as of Postfix version 2.3,  permit_mx_backup  no	longer
	      accepts the address when the local mail system is primary MX for
	      the recipient domain.  Exception: permit_mx_backup  accepts  the
	      address  when  it	 specifies an authorized destination (see per‐
	      mit_auth_destination for definition).

       ·      Limitation: mail may be rejected in  case	 of  a	temporary  DNS
	      lookup problem with Postfix prior to version 2.0.

       reject_non_fqdn_recipient
	      Reject  the  request  when  the RCPT TO address is not in fully-
	      qualified domain form, as required by the RFC.
	      The non_fqdn_reject_code parameter specifies the	response  code
	      for rejected requests (default: 504).

       reject_rhsbl_recipient rbl_domain=d.d.d.d
	      Reject  the request when the RCPT TO domain is listed with the A
	      record "d.d.d.d" under rbl_domain (Postfix version 2.1 and later
	      only).   If  no "=d.d.d.d" is specified, reject the request when
	      the RCPT TO domain is listed with any A record under rbl_domain.
	      The maps_rbl_reject_code parameter specifies the	response  code
	      for  rejected  requests  (default:  554);	 the default_rbl_reply
	      parameter	 specifies  the	 default   server   reply;   and   the
	      rbl_reply_maps  parameter	 specifies  tables with server replies
	      indexed by rbl_domain.  This feature  is	available  in  Postfix
	      version 2.0 and later.

       reject_unauth_destination
	      Reject the request unless one of the following is true:

       ·      Postfix  is  mail forwarder: the resolved RCPT TO domain matches
	      $relay_domains or a subdomain thereof, and contains  no  sender-
	      specified routing (user@elsewhere@domain),

       ·      Postfix  is  the	final destination: the resolved RCPT TO domain
	      matches  $mydestination,	$inet_interfaces,   $proxy_interfaces,
	      $virtual_alias_domains,  or  $virtual_mailbox_domains,  and con‐
	      tains no sender-specified routing (user@elsewhere@domain).
	       The relay_domains_reject_code parameter specifies the  response
	      code for rejected requests (default: 554).

       reject_unknown_recipient_domain
	      Reject the request when Postfix is not final destination for the
	      recipient domain, and the RCPT TO domain has  no	DNS  A	or  MX
	      record,  or  when	 it has a malformed MX record such as a record
	      with a zero-length MX hostname (Postfix version 2.3 and later).
	      The unknown_address_reject_code parameter specifies the  numeri‐
	      cal  response  code  for	rejected requests (default: 450).  The
	      response is always 450 in case of a temporary DNS error.
	      The  unknown_address_tempfail_action  parameter  specifies   the
	      action after a temporary DNS error (default: defer_if_permit).

       reject_unlisted_recipient  (with	 Postfix  version  2.0:	 check_recipi‐
       ent_maps)
	      Reject the request when the RCPT TO address is not listed in the
	      list   of	 valid	recipients  for	 its  domain  class.  See  the
	      smtpd_reject_unlisted_recipient	parameter   description	   for
	      details.	This feature is available in Postfix 2.1 and later.

       reject_unverified_recipient
	      Reject  the request when mail to the RCPT TO address is known to
	      bounce, or when the recipient address destination is not	reach‐
	      able.   Address  verification information is managed by the ver‐
	      ify(8) server;  see  the	ADDRESS_VERIFICATION_README  file  for
	      details.
	      The  unverified_recipient_reject_code  parameter	specifies  the
	      numerical response code when  an	address	 is  known  to	bounce
	      (default: 450, change into 550 when you are confident that it is
	      safe to do so).
	      The  unverified_recipient_defer_code  parameter  specifies   the
	      numerical	 response  code	 when an address probe failed due to a
	      temporary problem (default: 450).
	      The unverified_recipient_tempfail_action parameter specifies the
	      action  after  addres  probe  failure due to a temporary problem
	      (default: defer_if_permit).
	      This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

       ·      Generic restrictions that can be used in any SMTP	 command  con‐
	      text, described under smtpd_client_restrictions.

       ·      SMTP    command	 specific    restrictions    described	 under
	      smtpd_client_restrictions,      smtpd_helo_restrictions	   and
	      smtpd_sender_restrictions.

       Example:

       smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination

smtpd_reject_unlisted_recipient (default: yes)
       Request that the Postfix SMTP server rejects mail for unknown recipient
       addresses,  even	 when  no  explicit  reject_unlisted_recipient	access
       restriction  is specified. This prevents the Postfix queue from filling
       up with undeliverable MAILER-DAEMON messages.

       An address is always considered "known" when it	matches	 a  virtual(5)
       alias or a canonical(5) mapping.

       ·      The recipient domain matches $mydestination, $inet_interfaces or
	      $proxy_interfaces,  but  the  recipient	is   not   listed   in
	      $local_recipient_maps, and $local_recipient_maps is not null.

       ·      The  recipient  domain  matches  $virtual_alias_domains  but the
	      recipient is not listed in $virtual_alias_maps.

       ·      The recipient domain matches  $virtual_mailbox_domains  but  the
	      recipient	 is  not  listed  in  $virtual_mailbox_maps, and $vir‐
	      tual_mailbox_maps is not null.

       ·      The recipient domain matches $relay_domains but the recipient is
	      not  listed  in $relay_recipient_maps, and $relay_recipient_maps
	      is not null.

       This feature is available in Postfix 2.1 and later.

smtpd_reject_unlisted_sender (default: no)
       Request that the Postfix SMTP server rejects mail from  unknown	sender
       addresses, even when no explicit reject_unlisted_sender access restric‐
       tion is specified. This can slow down an explosion of forged mail  from
       worms or viruses.

       An  address  is	always considered "known" when it matches a virtual(5)
       alias or a canonical(5) mapping.

       ·      The sender domain matches	 $mydestination,  $inet_interfaces  or
	      $proxy_interfaces, but the sender is not listed in $local_recip‐
	      ient_maps, and $local_recipient_maps is not null.

       ·      The sender domain matches $virtual_alias_domains but the	sender
	      is not listed in $virtual_alias_maps.

       ·      The  sender  domain  matches  $virtual_mailbox_domains  but  the
	      sender  is  not  listed  in  $virtual_mailbox_maps,  and	 $vir‐
	      tual_mailbox_maps is not null.

       ·      The  sender  domain matches $relay_domains but the sender is not
	      listed in $relay_recipient_maps,	and  $relay_recipient_maps  is
	      not null.

       This feature is available in Postfix 2.1 and later.

smtpd_restriction_classes (default: empty)
       User-defined aliases for groups of access restrictions. The aliases can
       be specified in smtpd_recipient_restrictions etc., and  on  the	right-
       hand side of a Postfix access(5) table.

       One  major  application	is for implementing per-recipient UCE control.
       See the RESTRICTION_CLASS_README document for other examples.

smtpd_sasl_application_name (default: smtpd)
       The application name that the Postfix SMTP server uses for SASL	server
       initialization.	This controls the name of the SASL configuration file.
       The default value is smtpd, corresponding to a SASL configuration  file
       named smtpd.conf.

       This  feature  is available in Postfix 2.1 and 2.2. With Postfix 2.3 it
       was renamed to smtpd_sasl_path.

smtpd_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix SMTP server. By default,  the
       Postfix SMTP server does not use authentication.

       If a remote SMTP client is authenticated, the permit_sasl_authenticated
       access restriction can be used to permit relay access, like this:

	   smtpd_recipient_restrictions =
	       permit_mynetworks, permit_sasl_authenticated, ...

       To reject all SMTP connections from  unauthenticated  clients,  specify
       "smtpd_delay_reject = yes" (which is the default) and use:

	   smtpd_client_restrictions = permit_sasl_authenticated, reject

       See the SASL_README file for SASL configuration and operation details.

smtpd_sasl_authenticated_header (default: no)
       Report  the  SASL authenticated user name in the smtpd(8) Received mes‐
       sage header.

       This feature is available in Postfix 2.3 and later.

smtpd_sasl_exceptions_networks (default: empty)
       What remote SMTP clients the Postfix SMTP server will  not  offer  AUTH
       support to.

       Some  clients  (Netscape	 4  at	least)	have a bug that causes them to
       require a login and password whenever AUTH  is  offered,	 whether  it's
       necessary  or  not.  To work around this, specify, for example, $mynet‐
       works to prevent Postfix from offering AUTH to local clients.

       Specify a list of network/netmask patterns, separated by commas	and/or
       whitespace.  The	 mask specifies the number of bits in the network part
       of a host address. You can also "/file/name" or "type:table"  patterns.
       A  "/file/name"	pattern	 is  replaced  by its contents; a "type:table"
       lookup table is matched when a table entry matches a lookup string (the
       lookup  result  is  ignored).  Continue long lines by starting the next
       line with whitespace. Specify "!pattern" to exclude an address or  net‐
       work  block from the list.  The form "!/file/name" is supported only in
       Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside	[]  in
       the  smtpd_sasl_exceptions_networks  value, and in files specified with
       "/file/name".  IP version 6 addresses contain the  ":"  character,  and
       would otherwise be confused with a "type:table" pattern.

       Example:

       smtpd_sasl_exceptions_networks = $mynetworks

       This feature is available in Postfix 2.1 and later.

smtpd_sasl_local_domain (default: empty)
       The name of the Postfix SMTP server's local SASL authentication realm.

       By default, the local authentication realm name is the null string.

       Examples:

       smtpd_sasl_local_domain = $mydomain
       smtpd_sasl_local_domain = $myhostname

smtpd_sasl_path (default: smtpd)
       Implementation-specific information that the Postfix SMTP server passes
       through to the  SASL  plug-in  implementation  that  is	selected  with
       smtpd_sasl_type.	  Typically this specifies the name of a configuration
       file or rendezvous point.

       This feature is available in Postfix 2.3 and later. In earlier releases
       it was called smtpd_sasl_application_name.

smtpd_sasl_security_options (default: noanonymous)
       Postfix	SMTP  server SASL security options; as of Postfix 2.3 the list
       of available features depends on the SASL server implementation that is
       selected with smtpd_sasl_type.

       The  following  security features are defined for the cyrus server SASL
       implementation:

       Restrict what authentication mechanisms the Postfix  SMTP  server  will
       offer  to  the client.  The list of available authentication mechanisms
       is system dependent.

       Specify zero or more of the following:

       noplaintext
	      Disallow methods that use plaintext passwords.

       noactive
	      Disallow methods subject to active (non-dictionary) attack.

       nodictionary
	      Disallow methods subject to passive (dictionary) attack.

       noanonymous
	      Disallow methods that allow anonymous authentication.

       forward_secrecy
	      Only allow methods that support forward secrecy (Dovecot only).

       mutual_auth
	      Only allow  methods  that	 provide  mutual  authentication  (not
	      available with Cyrus SASL version 1).

       By default, the Postfix SMTP server accepts plaintext passwords but not
       anonymous logins.

       Warning: it appears that clients	 try  authentication  methods  in  the
       order  as  advertised  by  the  server (e.g., PLAIN ANONYMOUS CRAM-MD5)
       which means that if you disable plaintext passwords, clients  will  log
       in  anonymously, even when they should be able to use CRAM-MD5.	So, if
       you disable plaintext logins, disable anonymous	logins	too.   Postfix
       treats anonymous login as no authentication.

       Example:

       smtpd_sasl_security_options = noanonymous, noplaintext

smtpd_sasl_tls_security_options (default: $smtpd_sasl_security_options)
       The  SASL  authentication security options that the Postfix SMTP server
       uses for TLS encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtpd_sasl_type (default: cyrus)
       The SASL plug-in type that the  Postfix	SMTP  server  should  use  for
       authentication.	The  available types are listed with the "postconf -a"
       command.

       This feature is available in Postfix 2.3 and later.

smtpd_sender_login_maps (default: empty)
       Optional lookup table with the SASL login names that own	 sender	 (MAIL
       FROM) addresses.

       Specify	zero  or  more	"type:table"  lookup tables. With lookups from
       indexed files such as DB or DBM, or from networked tables such as  NIS,
       LDAP  or	 SQL,  the  following search operations are done with a sender
       address of user@domain:

       1) user@domain
	      This table lookup is always done and has the highest precedence.

       2) user
	      This table lookup is done only  when  the	 domain	 part  of  the
	      sender  address  matches $myorigin, $mydestination, $inet_inter‐
	      faces or $proxy_interfaces.

       3) @domain
	      This table lookup is done last and has the lowest precedence.

       In all cases the result of table lookup must be either "not found" or a
       list of SASL login names separated by comma and/or whitespace.

smtpd_sender_restrictions (default: empty)
       Optional	 restrictions that the Postfix SMTP server applies in the con‐
       text of	the  MAIL  FROM	 command.   See	 SMTPD_ACCESS_README,  section
       "Delayed	 evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       The default is to permit everything.

       Specify a list of restrictions, separated by commas and/or  whitespace.
       Continue	 long  lines  by  starting  the	 next  line  with  whitespace.
       Restrictions are applied in the order as specified; the first  restric‐
       tion that matches wins.

       The  following restrictions are specific to the sender address received
       with the MAIL FROM command.

       check_sender_access type:table
	      Search the  specified  access(5)	database  for  the  MAIL  FROM
	      address,	domain, parent domains, or localpart@, and execute the
	      corresponding action.

       check_sender_mx_access type:table
	      Search the specified access(5) database for the MX hosts for the
	      MAIL  FROM address, and execute the corresponding action.	 Note:
	      a result of "OK" is not allowed for safety reasons. Instead, use
	      DUNNO  in order to exclude specific hosts from blacklists.  This
	      feature is available in Postfix 2.1 and later.

       check_sender_ns_access type:table
	      Search the specified access(5) database for the DNS servers  for
	      the  MAIL	 FROM  address,	 and execute the corresponding action.
	      Note: a result of	 "OK"  is  not	allowed	 for  safety  reasons.
	      Instead,	use  DUNNO  in	order  to  exclude specific hosts from
	      blacklists.  This feature is available in Postfix 2.1 and later.

       reject_authenticated_sender_login_mismatch
	      Enforces	the   reject_sender_login_mismatch   restriction   for
	      authenticated clients only. This feature is available in Postfix
	      version 2.1 and later.

       reject_non_fqdn_sender
	      Reject the request when the MAIL FROM address is not  in	fully-
	      qualified domain form, as required by the RFC.
	      The  non_fqdn_reject_code	 parameter specifies the response code
	      for rejected requests (default: 504).

       reject_rhsbl_sender rbl_domain=d.d.d.d
	      Reject the request when the MAIL FROM domain is listed with  the
	      A	 record	 "d.d.d.d"  under  rbl_domain (Postfix version 2.1 and
	      later only).  If no "=d.d.d.d" is specified, reject the  request
	      when  the	 MAIL  FROM  domain  is listed with any A record under
	      rbl_domain.
	      The maps_rbl_reject_code parameter specifies the	response  code
	      for  rejected  requests  (default:   554); the default_rbl_reply
	      parameter	 specifies  the	 default   server   reply;   and   the
	      rbl_reply_maps  parameter	 specifies  tables with server replies
	      indexed by rbl_domain.  This feature is available in Postfix 2.0
	      and later.

       reject_sender_login_mismatch
	      Reject  the  request  when $smtpd_sender_login_maps specifies an
	      owner for the MAIL FROM address, but the client  is  not	(SASL)
	      logged in as that MAIL FROM address owner; or when the client is
	      (SASL) logged in, but the client login name doesn't own the MAIL
	      FROM address according to $smtpd_sender_login_maps.

       reject_unauthenticated_sender_login_mismatch
	      Enforces	the reject_sender_login_mismatch restriction for unau‐
	      thenticated clients only. This feature is available  in  Postfix
	      version 2.1 and later.

       reject_unknown_sender_domain
	      Reject the request when Postfix is not final destination for the
	      sender address, and the MAIL FROM address has no	DNS  A	or  MX
	      record,  or  when	 it has a malformed MX record such as a record
	      with a zero-length MX hostname (Postfix version 2.3 and later).
	      The unknown_address_reject_code parameter specifies the  numeri‐
	      cal  response  code  for	rejected requests (default: 450).  The
	      response is always 450 in case of a temporary DNS error.
	      The  unknown_address_tempfail_action  parameter  specifies   the
	      action after a temporary DNS error (default: defer_if_permit).

       reject_unlisted_sender
	      Reject  the  request when the MAIL FROM address is not listed in
	      the list of valid recipients  for	 its  domain  class.  See  the
	      smtpd_reject_unlisted_sender  parameter description for details.
	      This feature is available in Postfix 2.1 and later.

       reject_unverified_sender
	      Reject the request when mail to the MAIL FROM address  is	 known
	      to  bounce, or when the sender address destination is not reach‐
	      able.  Address verification information is managed by  the  ver‐
	      ify(8)  server;  see  the	 ADDRESS_VERIFICATION_README  file for
	      details.
	      The unverified_sender_reject_code parameter specifies the numer‐
	      ical  response code when an address is known to bounce (default:
	      450, change into 550 when you are confident that it is  safe  to
	      do so).
	      The   unverified_sender_defer_code   specifies   the   numerical
	      response code when an address address probe failed due to a tem‐
	      porary problem (default: 450).
	      The  unverified_sender_tempfail_action  parameter	 specifies the
	      action after address probe failure due to	 a  temporary  problem
	      (default: defer_if_permit).
	      This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

       ·      Generic  restrictions  that can be used in any SMTP command con‐
	      text, described under smtpd_client_restrictions.

       ·      SMTP   command	specific    restrictions    described	 under
	      smtpd_client_restrictions and smtpd_helo_restrictions.

       ·      SMTP command specific restrictions described under smtpd_recipi‐
	      ent_restrictions. When recipient restrictions are	 listed	 under
	      smtpd_sender_restrictions,    they   have	  effect   only	  with
	      "smtpd_delay_reject = yes", so  that  $smtpd_sender_restrictions
	      is evaluated at the time of the RCPT TO command.

       Examples:

       smtpd_sender_restrictions = reject_unknown_sender_domain
       smtpd_sender_restrictions = reject_unknown_sender_domain,
	   check_sender_access hash:$config_directory/access

smtpd_service_name (default: smtpd)
       The  internal  service  that postscreen(8) forwards allowed connections
       to. In a future version there may be different classes of SMTP service.

       This feature is available in Postfix 2.8.

smtpd_soft_error_limit (default: 10)
       The number of errors a remote SMTP client is allowed  to	 make  without
       delivering  mail	 before	 the  Postfix  SMTP  server slows down all its
       responses.

       ·      With Postfix version 2.1 and  later,  the	 Postfix  SMTP	server
	      delays all responses by $smtpd_error_sleep_time seconds.

       ·      With  Postfix  versions 2.0 and earlier, the Postfix SMTP server
	      delays all responses by (number of errors) seconds.

smtpd_starttls_timeout (default: 300s)
       The time limit for Postfix SMTP server write and read operations during
       TLS startup and shutdown handshake procedures.

       This feature is available in Postfix 2.2 and later.

smtpd_timeout (default: normal: 300s, overload: 10s)
       The  time  limit	 for  sending  a  Postfix SMTP server response and for
       receiving a remote SMTP client request. Normally the default  limit  is
       300s,  but  it changes under overload to just 10s. With Postfix 2.5 and
       earlier, the SMTP server always uses a time limit of 300s by default.

       Note: if you set SMTP time limits to very large values you may have  to
       update the global ipc_timeout parameter.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtpd_tls_CAfile (default: empty)
       A file containing (PEM format) CA certificates of root CAs  trusted  to
       sign either remote SMTP client certificates or intermediate CA certifi‐
       cates.  These are loaded into memory before the smtpd(8) server	enters
       the  chroot  jail.  If  the  number of trusted roots is large, consider
       using smtpd_tls_CApath instead, but note that the latter directory must
       be  present in the chroot jail if the smtpd(8) server is chrooted. This
       file may also be used to augment the server  certificate	 trust	chain,
       but it is best to include all the required certificates directly in the
       server certificate file.

       Specify "tls_append_default_CA = no" to prevent Postfix from  appending
       the system-supplied default CAs and trusting third-party certificates.

       By  default  (see  smtpd_tls_ask_ccert),	 client	 certificates  are not
       requested, and smtpd_tls_CAfile should remain empty. If you do make use
       of  client  certificates, the distinguished names (DNs) of the certifi‐
       cate authorities listed in smtpd_tls_CAfile are sent to the remote SMTP
       client  in  the	client certificate request message. MUAs with multiple
       client certificates may use the list of preferred certificate  authori‐
       ties  to	 select	 the  correct client certificate.  You may want to put
       your "preferred" CA or CAs in this file, and install other trusted  CAs
       in $smtpd_tls_CApath.

       Example:

       smtpd_tls_CAfile = $config_directory/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_CApath (default: empty)
       A directory containing (PEM format) CA certificates of root CAs trusted
       to sign either remote SMTP client certificates or intermediate CA  cer‐
       tificates. Do not forget to create the necessary "hash" links with, for
       example, "$OPENSSL_HOME/bin/c_rehash /usr/local/etc/postfix/certs".  To
       use smtpd_tls_CApath in chroot mode, this directory (or a copy) must be
       inside the chroot jail.

       Specify "tls_append_default_CA = no" to prevent Postfix from  appending
       the system-supplied default CAs and trusting third-party certificates.

       By  default  (see  smtpd_tls_ask_ccert),	 client	 certificates  are not
       requested, and smtpd_tls_CApath should remain  empty.  In  contrast  to
       smtpd_tls_CAfile,   DNs	 of   certificate   authorities	 installed  in
       $smtpd_tls_CApath are not included in the  client  certificate  request
       message.	 MUAs  with  multiple  client certificates may use the list of
       preferred certificate authorities to select the correct client certifi‐
       cate.	You   may   want   to  put  your  "preferred"  CA  or  CAs  in
       $smtpd_tls_CAfile,  and	install	  the	remaining   trusted   CAs   in
       $smtpd_tls_CApath.

       Example:

       smtpd_tls_CApath = $config_directory/certs

       This feature is available in Postfix 2.2 and later.

smtpd_tls_always_issue_session_ids (default: yes)
       Force  the Postfix SMTP server to issue a TLS session id, even when TLS
       session caching	is  turned  off	 (smtpd_tls_session_cache_database  is
       empty). This behavior is compatible with Postfix < 2.3.

       With  Postfix 2.3 and later the Postfix SMTP server can disable session
       id generation when TLS  session	caching	 is  turned  off.  This	 keeps
       clients from caching sessions that almost certainly cannot be re-used.

       By  default,  the Postfix SMTP server always generates TLS session ids.
       This works around a known defect in mail client applications such as MS
       Outlook, and may also prevent interoperability issues with other MTAs.

       Example:

       smtpd_tls_always_issue_session_ids = no

       This feature is available in Postfix 2.3 and later.

smtpd_tls_ask_ccert (default: no)
       Ask  a remote SMTP client for a client certificate. This information is
       needed for certificate based mail relaying with, for example, the  per‐
       mit_tls_clientcerts feature.

       Some clients such as Netscape will either complain if no certificate is
       available (for the list of CAs in $smtpd_tls_CAfile) or will offer mul‐
       tiple client certificates to choose from. This may be annoying, so this
       option is "off" by default.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_auth_only (default: no)
       When TLS encryption is optional in the  Postfix	SMTP  server,  do  not
       announce or accept SASL authentication over unencrypted connections.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_ccert_verifydepth (default: 9)
       The  verification depth for remote SMTP client certificates. A depth of
       1 is sufficient if the issuing CA is listed in a local CA file.

       The default verification depth is 9 (the OpenSSL default) for  compati‐
       bility with earlier Postfix behavior. Prior to Postfix 2.5, the default
       value was 5, but the limit was not actually enforced. If you  have  set
       this  to	 a  lower  non-default	value,	certificates with longer trust
       chains may now fail to verify. Certificate chains with 1 or 2  CAs  are
       common,	deeper	chains	are  more  rare and any number between 5 and 9
       should suffice in practice. You can choose a lower number if, for exam‐
       ple,  you  trust	 certificates directly signed by an issuing CA but not
       any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_cert_file (default: empty)
       File with the Postfix SMTP server RSA certificate in PEM format.	  This
       file may also contain the Postfix SMTP server private RSA key.

       Public  Internet	 MX hosts without certificates signed by a "reputable"
       CA must generate, and be prepared to present to most clients,  a	 self-
       signed or private-CA signed certificate. The client will not be able to
       authenticate the server, but unless it is running Postfix 2.3 or	 simi‐
       lar software, it will still insist on a server certificate.

       For servers that are not public Internet MX hosts, Postfix 2.3 supports
       configurations with no certificates. This entails the use of  just  the
       anonymous TLS ciphers, which are not supported by typical SMTP clients.
       Since such clients will not, as a rule, fall back to plain text after a
       TLS  handshake failure, the server will be unable to receive email from
       TLS enabled clients. To avoid accidental configurations	with  no  cer‐
       tificates, Postfix 2.3 enables certificate-less operation only when the
       administrator  explicitly  sets	"smtpd_tls_cert_file  =	 none".	  This
       ensures	that new Postfix configurations will not accidentally run with
       no certificates.

       Both RSA and DSA certificates  are  supported.	When  both  types  are
       present, the cipher used determines which certificate will be presented
       to the client.  For Netscape and OpenSSL clients without special cipher
       choices the RSA certificate is preferred.

       To  enable  a remote SMTP client to verify the Postfix SMTP server cer‐
       tificate, the issuing CA certificates must be  made  available  to  the
       client. You should include the required certificates in the server cer‐
       tificate file, the server certificate first,  then  the	issuing	 CA(s)
       (bottom-up order).

       Example: the certificate for "server.example.com" was issued by "inter‐
       mediate CA" which itself has a certificate of "root  CA".   Create  the
       server.pem   file   with	  "cat	 server_cert.pem   intermediate_CA.pem
       root_CA.pem > server.pem".

       If you also want to verify client certificates issued by these CAs, you
       can  add	 the CA certificates to the smtpd_tls_CAfile, in which case it
       is  not	necessary  to  have  them  in	the   smtpd_tls_cert_file   or
       smtpd_tls_dcert_file.

       A certificate supplied here must be usable as an SSL server certificate
       and hence pass the "openssl verify -purpose sslserver ..." test.

       Example:

       smtpd_tls_cert_file = $config_directory/server.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_cipherlist (default: empty)
       Obsolete Postfix < 2.3 control for the Postfix SMTP server  TLS	cipher
       list.  It  is  easy  to create inter-operability problems by choosing a
       non-default cipher list. Do not use a non-default TLS cipherlist for MX
       hosts on the public Internet. Clients that begin the TLS handshake, but
       are unable to agree on a common cipher, may not be  able	 to  send  any
       email  to  the  SMTP server. Using a restricted cipher list may be more
       appropriate for a dedicated MSA or an internal mailhub, where  one  can
       exert some control over the TLS software and settings of the connecting
       clients.

       Note: do not use "" quotes around the parameter value.

       This feature is available with Postfix version 2.2. It is not used with
       Postfix 2.3 and later; use smtpd_tls_mandatory_ciphers instead.

smtpd_tls_ciphers (default: export)
       The minimum TLS cipher grade that the Postfix SMTP server will use with
       opportunistic	TLS    encryption.    Cipher	types	 listed	    in
       smtpd_tls_exclude_ciphers  are excluded from the base definition of the
       selected cipher grade.  The  default  value  "export"  ensures  maximum
       inter-operability.  Because  encryption	is optional, stronger controls
       are not appropriate, and this setting SHOULD NOT be changed unless  the
       change is essential.

       When   TLS   is	 mandatory   the   cipher  grade  is  chosen  via  the
       smtpd_tls_mandatory_ciphers configuration parameter, see there for syn‐
       tax details.

       Example:
       smtpd_tls_ciphers = export

       This  feature is available in Postfix 2.6 and later. With earlier Post‐
       fix releases only the smtpd_tls_mandatory_ciphers parameter  is	imple‐
       mented, and opportunistic TLS always uses "export" or better (i.e. all)
       ciphers.

smtpd_tls_dcert_file (default: empty)
       File with the Postfix SMTP server DSA certificate in PEM format.	  This
       file may also contain the Postfix SMTP server private DSA key.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_dcert_file = $config_directory/server-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_dh1024_param_file (default: empty)
       File  with  DH  parameters that the Postfix SMTP server should use with
       EDH ciphers.

       Instead of using the exact same	parameter  sets	 as  distributed  with
       other  TLS  packages,  it  is  more  secure to generate your own set of
       parameters with something like the following command:

	   openssl gendh -out /usr/local/etc/postfix/dh_1024.pem -2 1024

       Your actual source for entropy may differ. Some systems have  /dev/ran‐
       dom; on other system you may consider using the "Entropy Gathering Dae‐
       mon EGD", available at http://egd.sourceforge.net/

       Example:

       smtpd_tls_dh1024_param_file = $config_directory/dh_1024.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dh512_param_file (default: empty)
       File with DH parameters that the Postfix SMTP server  should  use  with
       EDH ciphers.

       See  also the discussion under the smtpd_tls_dh1024_param_file configu‐
       ration parameter.

       Example:

       smtpd_tls_dh512_param_file = $config_directory/dh_512.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dkey_file (default: $smtpd_tls_dcert_file)
       File with the Postfix SMTP server DSA private key in PEM format.	  This
       file  may be combined with the Postfix SMTP server DSA certificate file
       specified with $smtpd_tls_dcert_file.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_eccert_file (default: empty)
       File with the Postfix SMTP server  ECDSA	 certificate  in  PEM  format.
       This file may also contain the Postfix SMTP server private ECDSA key.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_eccert_file = $config_directory/ecdsa-scert.pem

       This  feature  is  available  in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

smtpd_tls_eckey_file (default: $smtpd_tls_eccert_file)
       File with the Postfix SMTP server ECDSA	private	 key  in  PEM  format.
       This  file  may be combined with the Postfix SMTP server ECDSA certifi‐
       cate file specified with $smtpd_tls_eccert_file.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.6 and  later,  when  Postfix  is
       compiled and linked with OpenSSL 1.0.0 or later.

smtpd_tls_eecdh_grade (default: see postconf -d output)
       The  Postfix  SMTP  server  security grade for ephemeral elliptic-curve
       Diffie-Hellman (EECDH) key exchange.

       The available choices are:

       none   Don't use EECDH. Ciphers based on EECDH  key  exchange  will  be
	      disabled.	 This  is  the	default	 in  official Postfix releases
	      (mail_version = major.minor.patchlevel).

       strong Use EECDH with approximately 128 bits of security at  a  reason‐
	      able  computational  cost.  This	is  the	 current best-practice
	      trade-off between security and computational efficiency. This is
	      the   default  in	 Postfix  snapshot  releases  (mail_version  =
	      major.minor-releasedate).

       ultra  Use EECDH with approximately 192 bits of	security  at  computa‐
	      tional  cost  that  is  approximately  twice  as high as 128 bit
	      strength ECC. Barring significant progress in attacks on	ellip‐
	      tic  curve  crypto-systems, the "strong" curve is sufficient for
	      most users.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 1.0.0 or later.

smtpd_tls_exclude_ciphers (default: empty)
       List  of ciphers or cipher types to exclude from the SMTP server cipher
       list at all TLS security levels. Excluding  valid  ciphers  can	create
       interoperability	 problems.  DO NOT exclude ciphers unless it is essen‐
       tial to do so. This is not an OpenSSL cipherlist; it is a  simple  list
       separated  by  whitespace  and/or  commas.  The	elements  are a single
       cipher, or one or more "+" separated cipher properties, in  which  case
       only ciphers matching all the properties are excluded.

       Examples (some of these will cause problems):

	   smtpd_tls_exclude_ciphers = aNULL
	   smtpd_tls_exclude_ciphers = MD5, DES
	   smtpd_tls_exclude_ciphers = DES+MD5
	   smtpd_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
	   smtpd_tls_exclude_ciphers = kEDH+aRSA

       The first setting disables anonymous ciphers. The next setting disables
       ciphers that use the MD5 digest algorithm or the (single)  DES  encryp‐
       tion  algorithm. The next setting disables ciphers that use MD5 and DES
       together.  The next setting disables the two ciphers  "AES256-SHA"  and
       "DES-CBC3-MD5".	The  last  setting disables ciphers that use "EDH" key
       exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtpd_tls_fingerprint_digest (default: md5)
       The message digest algorithm used to construct client-certificate  fin‐
       gerprints   for	 check_ccert_access  and  permit_tls_clientcerts.  The
       default algorithm is md5,  for  backwards  compatibility	 with  Postfix
       releases prior to 2.5.

       The  best practice algorithm is now sha1. Recent advances in hash func‐
       tion cryptanalysis have led to md5 being deprecated in favor  of	 sha1.
       However,	 as  long  as  there  are  no known "second pre-image" attacks
       against md5, its use in this context can still be considered safe.

       While additional digest algorithms are often available  with  OpenSSL's
       libcrypto, only those used by libssl in SSL cipher suites are available
       to Postfix. For now this means just md5 or sha1.

       To find the fingerprint of a specific certificate file, with a specific
       digest algorithm, run:

	   $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The  text  to  the  right  of "=" sign is the desired fingerprint.  For
       example:

	   $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
	   SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       Example: client-certificate access table, with sha1 fingerprints:

	   /usr/local/etc/postfix/main.cf:
	       smtpd_tls_fingerprint_digest = sha1
	       smtpd_client_restrictions =
		   check_ccert_access hash:$config_directory/access,
		   reject
	   /usr/local/etc/postfix/access:
	       # Action folded to next line...
	       AF:88:7C:AD:51:95:6F:36:96:F6:01:FB:2E:48:CD:AB:49:25:A2:3B
		   OK
	       85:16:78:FD:73:6E:CE:70:E0:31:5F:0D:3C:C8:6D:C4:2C:24:59:E1
		   permit_auth_destination

       This feature is available in Postfix 2.5 and later.

smtpd_tls_key_file (default: $smtpd_tls_cert_file)
       File with the Postfix SMTP server RSA private key in PEM format.	  This
       file  may be combined with the Postfix SMTP server RSA certificate file
       specified with $smtpd_tls_cert_file.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

smtpd_tls_loglevel (default: 0)
       Enable additional Postfix SMTP server logging of	 TLS  activity.	  Each
       logging	level  also includes the information that is logged at a lower
       logging level.

	      0 Disable logging of TLS activity.

	      1 Log TLS handshake and certificate information.

	      2 Log levels during TLS negotiation.

	      3 Log hexadecimal and ASCII dump of TLS negotiation process.

	      4 Also log hexadecimal and ASCII dump of	complete  transmission
	      after STARTTLS.

       Use  "smtpd_tls_loglevel = 3" only in case of problems. Use of loglevel
       4 is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_mandatory_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP server will use with
       mandatory  TLS encryption. The default grade ("medium") is sufficiently
       strong that any benefit from globally restricting  TLS  sessions	 to  a
       more  stringent	grade  is likely negligible, especially given the fact
       that many implementations still	do  not	 offer	any  stronger  ("high"
       grade)  ciphers,	 while	those  that  do,  will always use "high" grade
       ciphers. So insisting on "high" grade ciphers is generally counter-pro‐
       ductive.	 Allowing  "export"  or	 "low" ciphers is typically not a good
       idea, as	 systems  limited  to  just  these  are	 limited  to  obsolete
       browsers.  No  known SMTP clients fail to support at least one "medium"
       or "high" grade cipher.

       The following cipher grades are supported:

       export Enable "EXPORT" grade or stronger OpenSSL ciphers.  This is  the
	      most appropriate setting for public MX hosts, and is always used
	      with opportunistic TLS encryption. The underlying cipherlist  is
	      specified via the tls_export_cipherlist configuration parameter,
	      which you are strongly encouraged to not change.

       low    Enable "LOW" grade or stronger OpenSSL ciphers.  The  underlying
	      cipherlist is specified via the tls_low_cipherlist configuration
	      parameter, which you are strongly encouraged to not change.

       medium Enable "MEDIUM" grade or stronger	 OpenSSL  ciphers.  These  use
	      128-bit  or  longer  symmetric bulk-encryption keys. This is the
	      default minimum  strength	 for  mandatory	 TLS  encryption.  The
	      underlying cipherlist is specified via the tls_medium_cipherlist
	      configuration parameter, which you are  strongly	encouraged  to
	      not change.

       high   Enable   only  "HIGH"  grade  OpenSSL  ciphers.  The  underlying
	      cipherlist is specified via the  tls_high_cipherlist  configura‐
	      tion parameter, which you are strongly encouraged to not change.

       null   Enable  only the "NULL" OpenSSL ciphers, these provide authenti‐
	      cation without encryption.  This setting is only appropriate  in
	      the  rare case that all clients are prepared to use NULL ciphers
	      (not normally enabled in TLS clients). The underlying cipherlist
	      is  specified  via the tls_null_cipherlist configuration parame‐
	      ter, which you are strongly encouraged to not change.

       Cipher	types	listed	 in   smtpd_tls_mandatory_exclude_ciphers   or
       smtpd_tls_exclude_ciphers  are excluded from the base definition of the
       selected cipher grade. See smtpd_tls_ciphers for cipher	controls  that
       apply to opportunistic TLS.

       The  underlying cipherlists for grades other than "null" include anony‐
       mous ciphers, but these are automatically filtered out if the server is
       configured  to  ask  for client certificates.  You are very unlikely to
       need to take any steps to exclude anonymous ciphers, they are  excluded
       automatically  as required.  If you must exclude anonymous ciphers even
       when  Postfix  does  not	  need	 or   use   peer   certificates,   set
       "smtpd_tls_exclude_ciphers  = aNULL". To exclude anonymous ciphers only
       when  TLS  is  enforced,	 set  "smtpd_tls_mandatory_exclude_ciphers   =
       aNULL".

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_exclude_ciphers (default: empty)
       Additional  list	 of  ciphers  or cipher types to exclude from the SMTP
       server cipher list at mandatory TLS security levels. This list works in
       addition	 to  the exclusions listed with smtpd_tls_exclude_ciphers (see
       there for syntax details).

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_protocols (default: SSLv3, TLSv1)
       The SSL/TLS protocols accepted by the Postfix SMTP server  with	manda‐
       tory  TLS  encryption.  If  the	list is empty, the server supports all
       available SSL/TLS protocol versions.  A non-empty value is  a  list  of
       protocol names separated by whitespace, commas or colons. The supported
       protocol names are "SSLv2", "SSLv3" and "TLSv1", and are not case  sen‐
       sitive.

       With  Postfix >= 2.5 the parameter syntax is expanded to support proto‐
       col exclusions.	One  can  now  explicitly  exclude  SSLv2  by  setting
       "smtpd_tls_mandatory_protocols  =  !SSLv2".  To	exclude both SSLv2 and
       SSLv3 set "smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3". Listing the
       protocols  to  include, rather than protocols to exclude, is still sup‐
       ported, use the form you find more intuitive.

       Since SSL version 2 has known protocol weaknesses  and  is  now	depre‐
       cated,  the  default  setting  excludes	"SSLv2".   This	 means that by
       default, SSL version 2 will not	be  used  at  the  "encrypt"  security
       level.

       Example:

       smtpd_tls_mandatory_protocols = TLSv1
       # Alternative form with Postfix >= 2.5:
       smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.3 and later.

smtpd_tls_protocols (default: empty)
       List  of	 TLS  protocols	 that  the Postfix SMTP server will exclude or
       include with opportunistic TLS encryption.  This	 parameter  SHOULD  be
       left at its default empty value, allowing all protocols to be used with
       opportunistic TLS.

       In main.cf the values are separated by whitespace, commas or colons. An
       empty  value  means allow all protocols. The valid protocol names, (see
       \fBfBSSL_get_version(3)),  are  "SSLv2",	 "SSLv3"   and	 "TLSv1".   In
       smtp_tls_policy_maps  table  entries,  "protocols" attribute values are
       separated by a colon.

       To include a protocol list its name, to exclude	it,  prefix  the  name
       with  a	"!" character. To exclude SSLv2 even for opportunistic TLS set
       "smtpd_tls_protocols = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
       "smtpd_tls_protocols  =	!SSLv2, !SSLv3". Explicitly listing the proto‐
       cols to include, is supported, but not recommended. OpenSSL provides no
       mechanisms  for excluding protocols not known at compile-time. If Post‐
       fix is linked against an OpenSSL library that supports additional  pro‐
       tocol versions, they cannot be excluded using either syntax.

       Example:
       smtpd_tls_protocols = !SSLv2

       This feature is available in Postfix 2.6 and later.

smtpd_tls_received_header (default: no)
       Request	that the Postfix SMTP server produces Received:	 message head‐
       ers that include information about the protocol	and  cipher  used,  as
       well as the client CommonName and client certificate issuer CommonName.
       This is disabled by default, as the  information	 may  be  modified  in
       transit through other mail servers.  Only information that was recorded
       by the final destination can be trusted.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_req_ccert (default: no)
       With mandatory TLS encryption, require a	 trusted  remote  SMTP	client
       certificate  in order to allow TLS connections to proceed.  This option
       implies "smtpd_tls_ask_ccert = yes".

       When TLS encryption is optional, this setting is ignored with a warning
       written to the mail log.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_security_level (default: empty)
       The  SMTP  TLS  security level for the Postfix SMTP server; when a non-
       empty value  is	specified,  this  overrides  the  obsolete  parameters
       smtpd_use_tls  and  smtpd_enforce_tls.  This  parameter is ignored with
       "smtpd_tls_wrappermode = yes".

       Specify one of the following security levels:

       none   TLS will not be used.

       may    Opportunistic TLS: announce STARTTLS support  to	SMTP  clients,
	      but do not require that clients use TLS encryption.

       encrypt
	      Mandatory	 TLS  encryption:  announce  STARTTLS  support to SMTP
	      clients, and require that clients use TLS encryption.  According
	      to  RFC 2487 this MUST NOT be applied in case of a publicly-ref‐
	      erenced SMTP server. Instead, this option should be used only on
	      dedicated servers.

       Note  1:	 the  "fingerprint", "verify" and "secure" levels are not sup‐
       ported here.  The Postfix SMTP server logs a warning and uses "encrypt"
       instead.	 To verify SMTP client certificates, see TLS_README for a dis‐
       cussion	of  the	 smtpd_tls_ask_ccert,  smtpd_tls_req_ccert,  and  per‐
       mit_tls_clientcerts features.

       Note  2:	 The  parameter	 setting  "smtpd_tls_security_level = encrypt"
       implies "smtpd_tls_auth_only = yes".

       Note 3: when invoked via	 "sendmail  -bs",  Postfix  will  never	 offer
       STARTTLS	 due  to  insufficient privileges to access the server private
       key. This is intended behavior.

       This feature is available in Postfix 2.3 and later.

smtpd_tls_session_cache_database (default: empty)
       Name of the file containing the optional Postfix SMTP server  TLS  ses‐
       sion  cache. Specify a database type that supports enumeration, such as
       btree or sdbm; there is no need to support concurrent access.  The file
       is  created if it does not exist. The smtpd(8) daemon does not use this
       parameter directly, rather the cache is implemented indirectly  in  the
       tlsmgr(8)  daemon.  This	 means that per-smtpd-instance master.cf over‐
       rides of this parameter are not effective. Note, that each of the cache
       databases supported by tlsmgr(8) daemon: $smtpd_tls_session_cache_data‐
       base, $smtp_tls_session_cache_database (and with Postfix 2.3 and	 later
       $lmtp_tls_session_cache_database), needs to be stored separately. It is
       not at this time possible to store multiple caches in  a	 single	 data‐
       base.

       Note:  dbm  databases  are  not	suitable.  TLS session objects are too
       large.

       As of version 2.5, Postfix no longer uses root privileges when  opening
       this  file.  The	 file  should  now  be	stored under the Postfix-owned
       data_directory. As a migration aid, an attempt to open the file under a
       non-Postfix  directory  is  redirected to the Postfix-owned data_direc‐
       tory, and a warning is logged.

       Example:

       smtpd_tls_session_cache_database = btree:/var/lib/postfix/smtpd_scache

       This feature is available in Postfix 2.2 and later.

smtpd_tls_session_cache_timeout (default: 3600s)
       The expiration time of Postfix SMTP server TLS session  cache  informa‐
       tion.  A	 cache cleanup is performed periodically every $smtpd_tls_ses‐
       sion_cache_timeout seconds. As with  $smtpd_tls_session_cache_database,
       this  parameter	is  implemented	 in the tlsmgr(8) daemon and therefore
       per-smtpd-instance master.cf overrides are not possible.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_wrappermode (default: no)
       Run the Postfix SMTP server in the non-standard "wrapper" mode, instead
       of using the STARTTLS command.

       If  you	want  to  support  this service, enable a special port in mas‐
       ter.cf, and specify "-o smtpd_tls_wrappermode=yes" on the SMTP server's
       command line. Port 465 (smtps) was once chosen for this purpose.

       This feature is available in Postfix 2.2 and later.

smtpd_use_tls (default: no)
       Opportunistic  TLS:  announce  STARTTLS support to SMTP clients, but do
       not require that clients use TLS encryption.

       Note: when invoked via "sendmail -bs", Postfix will never offer	START‐
       TLS  due	 to  insufficient privileges to access the server private key.
       This is intended behavior.

       This feature is available in Postfix 2.2 and later.  With  Postfix  2.3
       and later use smtpd_tls_security_level instead.

soft_bounce (default: no)
       Safety  net to keep mail queued that would otherwise be returned to the
       sender.	This parameter disables locally-generated  bounces,  and  pre‐
       vents  the  Postfix  SMTP  server  from	rejecting mail permanently, by
       changing 5xx reply codes into 4xx.  However, soft_bounce is no cure for
       address rewriting mistakes or mail routing mistakes.

       Example:

       soft_bounce = yes

stale_lock_time (default: 500s)
       The  time  after	 which	a stale exclusive mailbox lockfile is removed.
       This is used for delivery to file or mailbox.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

stress (default: empty)
       This feature is documented in the STRESS_README document.

       This feature is available in Postfix 2.5 and later.

strict_7bit_headers (default: no)
       Reject  mail  with 8-bit text in message headers. This blocks mail from
       poorly written applications.

       This feature should not be enabled on a general	purpose	 mail  server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime (default: no)
       Enable both strict_7bit_headers and strict_8bitmime_body.

       This  feature  should  not be enabled on a general purpose mail server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime_body (default: no)
       Reject 8-bit message body text  without	8-bit  MIME  content  encoding
       information.  This blocks mail from poorly written applications.

       Unfortunately,  this  also rejects majordomo approval requests when the
       included request contains valid 8-bit MIME mail, and it rejects bounces
       from  mailers  that do not MIME encapsulate 8-bit content (for example,
       bounces from qmail or from old versions of Postfix).

       This feature should not be enabled on a general	purpose	 mail  server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_mailbox_ownership (default: yes)
       Defer  delivery when a mailbox file is not owned by its recipient.  The
       default setting is not backwards compatible.

       This feature is available in Postfix 2.5.3 and later.

strict_mime_encoding_domain (default: no)
       Reject mail with invalid Content-Transfer-Encoding: information for the
       message/*  or  multipart/*  MIME	 content types.	 This blocks mail from
       poorly written software.

       This feature should not be enabled on a general	purpose	 mail  server,
       because it will reject mail after a single violation.

       This feature is available in Postfix 2.0 and later.

strict_rfc821_envelopes (default: no)
       Require	that addresses received in SMTP MAIL FROM and RCPT TO commands
       are enclosed with <>, and that those addresses do not contain  RFC  822
       style  comments	or phrases.  This stops mail from poorly written soft‐
       ware.

       By default, the Postfix SMTP server accepts RFC 822 syntax in MAIL FROM
       and RCPT TO addresses.

sun_mailtool_compatibility (default: no)
       Obsolete	 SUN  mailtool	compatibility  feature.	 Instead,  use	"mail‐
       box_delivery_lock = dotlock".

swap_bangpath (default: yes)
       Enable the rewriting of "site!user" into "user@site".  This  is	neces‐
       sary  if	 your machine is connected to UUCP networks.  It is enabled by
       default.

       Note: with Postfix version 2.2, message header address  rewriting  hap‐
       pens only when one of the following conditions is true:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The  message  is	received  from	a  network client that matches
	      $local_header_rewrite_clients,

       ·      The  message   is	  received   from   the	  network,   and   the
	      remote_header_rewrite_domain  parameter  specifies  a  non-empty
	      value.

       To   get	  the	behavior   before   Postfix   version	2.2,   specify
       "local_header_rewrite_clients = static:all".

       Example:

       swap_bangpath = no

syslog_facility (default: mail)
       The  syslog  facility of Postfix logging. Specify a facility as defined
       in syslog.conf(5). The default facility is "mail".

       Warning: a non-default syslog_facility setting takes effect only	 after
       a  Postfix process has completed initialization.	 Errors during process
       initialization will be logged with the default facility.	 Examples  are
       errors  while  parsing  the  command  line  arguments, and errors while
       accessing the Postfix main.cf configuration file.

syslog_name (default: see postconf -d output)
       The mail system name that is prepended to the process  name  in	syslog
       records, so that "smtpd" becomes, for example, "postfix/smtpd".

       Warning:	 a  non-default	 syslog_name setting takes effect only after a
       Postfix process has completed  initialization.  Errors  during  process
       initialization  will  be	 logged	 with  the  default name. Examples are
       errors while parsing the	 command  line	arguments,  and	 errors	 while
       accessing the Postfix main.cf configuration file.

tcp_windowsize (default: 0)
       An  optional  workaround	 for  routers  that  break TCP window scaling.
       Specify a value > 0 and < 65536 to enable this feature.	 With  Postfix
       TCP  servers  (smtpd(8),	 qmqpd(8)), this feature is implemented by the
       Postfix master(8) daemon.

       To change this parameter without stopping Postfix, you  need  to	 first
       terminate all Postfix TCP servers:

	   # postconf -e master_service_disable=inet
	   # postfix reload

       This  immediately  terminates all processes that accept network connec‐
       tions.  Next, you enable Postfix TCP servers with the updated  tcp_win‐
       dowsize setting:

	   # postconf -e tcp_windowsize=65535 master_service_disable=
	   # postfix reload

       If  you	skip  these  steps  with  a  running  Postfix system, then the
       tcp_windowsize change will work only for Postfix TCP clients  (smtp(8),
       lmtp(8)).

       This feature is available in Postfix 2.6 and later.

tls_append_default_CA (default: no)
       Append  the  system-supplied default certificate authority certificates
       to the ones specified with *_tls_CApath or *_tls_CAfile.	  The  default
       is  "no";  this prevents Postfix from trusting third-party certificates
       and giving them relay permission with permit_tls_all_clientcerts.

       This feature is available in Postfix 2.4.15, 2.5.11, 2.6.8,  2.7.2  and
       later  versions.	 Specify  "tls_append_default_CA  = yes" for backwards
       compatibility, to avoid breaking certificate  verification  with	 sites
       that don't use permit_tls_all_clientcerts.

tls_daemon_random_bytes (default: 32)
       The  number  of pseudo-random bytes that an smtp(8) or smtpd(8) process
       requests from the tlsmgr(8) server in order to seed its internal pseudo
       random number generator (PRNG).	The default of 32 bytes (equivalent to
       256 bits) is sufficient to generate a 128bit (or 168bit) session key.

       This feature is available in Postfix 2.2 and later.

tls_eecdh_strong_curve (default: prime256v1)
       The elliptic  curve  used  by  the  SMTP	 server	 for  sensibly	strong
       ephemeral  ECDH	key  exchange.	This curve is used by the Postfix SMTP
       server when "smtpd_tls_eecdh_grade  =  strong".	The  phrase  "sensibly
       strong"	means  approximately  128-bit  security	 based	on  best known
       attacks. The selected curve must be implemented by OpenSSL (as reported
       by  ecparam(1) with the "-list_curves" option) and be one of the curves
       listed in Section 5.1.1 of RFC 4492. You should	not  generally	change
       this setting.

       This  default  curve  is	 specified  in NSA "Suite B" Cryptography (see
       http://www.nsa.gov/ia/industry/crypto_suite_b.cfm)   for	   information
       classified as SECRET.

       Note: elliptic curve names are poorly standardized; different standards
       groups are assigning different names to	the  same  underlying  curves.
       The curve with the X9.62 name "prime256v1" is also known under the SECG
       name "secp256r1", but OpenSSL does not recognize the latter name.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 1.0.0 or later.

tls_eecdh_ultra_curve (default: secp384r1)
       The  elliptic  curve  used  by  the  SMTP  server  for maximally strong
       ephemeral ECDH key exchange. This curve is used	by  the	 Postfix  SMTP
       server  when  "smtpd_tls_eecdh_grade  =	ultra".	 The phrase "maximally
       strong" means  approximately  192-bit  security	based  on  best	 known
       attacks.	 This additional strength comes at a significant computational
       cost, most users should instead set "smtpd_tls_eecdh_grade  =  strong".
       The  selected  curve  must  be  implemented  by OpenSSL (as reported by
       ecparam(1) with the "-list_curves" option) and be  one  of  the	curves
       listed  in  Section  5.1.1 of RFC 4492. You should not generally change
       this setting.

       This default "ultra" curve is specified in NSA "Suite  B"  Cryptography
       (see http://www.nsa.gov/ia/industry/crypto_suite_b.cfm) for information
       classified as TOP SECRET.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 1.0.0 or later.

tls_export_cipherlist (default: ALL:+RC4:@STRENGTH)
       The  OpenSSL  cipherlist	 for  "EXPORT"	or  higher grade ciphers. This
       defines	the  meaning  of  the  "export"	 setting  in  smtpd_tls_manda‐
       tory_ciphers,	 smtp_tls_mandatory_ciphers	and    lmtp_tls_manda‐
       tory_ciphers. This is the cipherlist for the opportunistic ("may")  TLS
       client  security	 level	and  is	 the  default  cipherlist for the SMTP
       server. You are strongly encouraged to not change  this	setting.  With
       OpenSSL	1.0.0 and later the cipherlist may start with an "aNULL:" pre‐
       fix, which restores the 0.9.8-compatible ordering of the aNULL  ciphers
       to the top of the list when they are enabled. This prefix is not needed
       with previous OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_high_cipherlist (default: ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)
       The OpenSSL cipherlist for "HIGH" grade ciphers. This defines the mean‐
       ing    of    the	  "high"   setting   in	  smtpd_tls_mandatory_ciphers,
       smtp_tls_mandatory_ciphers  and	lmtp_tls_mandatory_ciphers.  You   are
       strongly	 encouraged to not change this setting. With OpenSSL 1.0.0 and
       later the cipherlist may start with an "aNULL:" prefix, which  restores
       the  0.9.8-compatible  ordering	of the aNULL ciphers to the top of the
       list when they are enabled. This prefix is  not	needed	with  previous
       OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_low_cipherlist (default: ALL:!EXPORT:+RC4:@STRENGTH)
       The  OpenSSL cipherlist for "LOW" or higher grade ciphers. This defines
       the  meaning  of	 the  "low"  setting  in  smtpd_tls_mandatory_ciphers,
       smtp_tls_mandatory_ciphers   and	 lmtp_tls_mandatory_ciphers.  You  are
       strongly encouraged to not change this setting.	With OpenSSL 1.0.0 and
       later  the cipherlist may start with an "aNULL:" prefix, which restores
       the 0.9.8-compatible ordering of the aNULL ciphers to the  top  of  the
       list  when  they	 are  enabled. This prefix is not needed with previous
       OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_medium_cipherlist (default: ALL:!EXPORT:!LOW:+RC4:@STRENGTH)
       The OpenSSL cipherlist for  "MEDIUM"  or	 higher	 grade	ciphers.  This
       defines	the  meaning  of  the  "medium"	 setting  in  smtpd_tls_manda‐
       tory_ciphers,	smtp_tls_mandatory_ciphers     and     lmtp_tls_manda‐
       tory_ciphers.  This is the default cipherlist for mandatory TLS encryp‐
       tion in the TLS client (with anonymous ciphers disabled when  verifying
       server  certificates).  You  are strongly encouraged to not change this
       setting.	 With OpenSSL 1.0.0 and later the cipherlist may start with an
       "aNULL:"	 prefix,  which	 restores the 0.9.8-compatible ordering of the
       aNULL ciphers to the top of the list when they are enabled. This prefix
       is not needed with previous OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_null_cipherlist (default: eNULL:!aNULL)
       The  OpenSSL cipherlist for "NULL" grade ciphers that provide authenti‐
       cation without encryption. This defines the meaning of the "null"  set‐
       ting  in	 smtpd_mandatory_tls_ciphers,  smtp_tls_mandatory_ciphers  and
       lmtp_tls_mandatory_ciphers.  You are strongly encouraged to not	change
       this setting.

       This feature is available in Postfix 2.3 and later.

tls_random_bytes (default: 32)
       The  number  of bytes that tlsmgr(8) reads from $tls_random_source when
       (re)seeding the in-memory pseudo random number generator	 (PRNG)	 pool.
       The  default of 32 bytes (256 bits) is good enough for 128bit symmetric
       keys.  If using EGD or a device file, a maximum of 255 bytes is read.

       This feature is available in Postfix 2.2 and later.

tls_random_exchange_name (default: see postconf -d output)
       Name of the pseudo random number generator (PRNG) state	file  that  is
       maintained  by  tlsmgr(8).  The file is created when it does not exist,
       and its length is fixed at 1024 bytes.

       As of version 2.5, Postfix no longer uses root privileges when  opening
       this  file,  and	 the  default  file  location  was changed from ${con‐
       fig_directory}/prng_exch to ${data_directory}/prng_exch.	 As  a	migra‐
       tion  aid, an attempt to open the file under a non-Postfix directory is
       redirected to  the  Postfix-owned  data_directory,  and	a  warning  is
       logged.

       This feature is available in Postfix 2.2 and later.

tls_random_prng_update_period (default: 3600s)
       The  time between attempts by tlsmgr(8) to save the state of the pseudo
       random number generator (PRNG) to the  file  specified  with  $tls_ran‐
       dom_exchange_name.

       This feature is available in Postfix 2.2 and later.

tls_random_reseed_period (default: 3600s)
       The maximal time between attempts by tlsmgr(8) to re-seed the in-memory
       pseudo random number generator (PRNG) pool from external sources.   The
       actual  time  between re-seeding attempts is calculated using the PRNG,
       and is between 0 and the time specified.

       This feature is available in Postfix 2.2 and later.

tls_random_source (default: see postconf -d output)
       The external entropy source for the in-memory tlsmgr(8)	pseudo	random
       number generator (PRNG) pool. Be sure to specify a non-blocking source.
       If this source is not a regular file, the entropy source type  must  be
       prepended:   egd:/path/to/egd_socket  for  a source with EGD compatible
       socket interface, or dev:/path/to/device for a device file.

       Note: on OpenBSD systems specify /dev/arandom when  /dev/urandom	 gives
       timeout errors.

       This feature is available in Postfix 2.2 and later.

trace_service_name (default: trace)
       The  name  of  the  trace  service.  This service is implemented by the
       bounce(8) daemon and maintains a record of mail deliveries and produces
       a  mail	delivery report when verbose delivery is requested with "send‐
       mail -v".

       This feature is available in Postfix 2.1 and later.

transport_delivery_slot_cost (default: $default_delivery_slot_cost)
       A transport-specific override for the default_delivery_slot_cost param‐
       eter value, where transport is the master.cf name of the message deliv‐
       ery transport.

transport_delivery_slot_discount (default: $default_delivery_slot_discount)
       A transport-specific override  for  the	default_delivery_slot_discount
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

transport_delivery_slot_loan (default: $default_delivery_slot_loan)
       A transport-specific override for the default_delivery_slot_loan param‐
       eter value, where transport is the master.cf name of the message deliv‐
       ery transport.

transport_destination_concurrency_failed_cohort_limit (default:	 $default_des‐
       tination_concurrency_failed_cohort_limit)
       A   transport-specific  override	 for  the  default_destination_concur‐
       rency_failed_cohort_limit parameter value, where transport is the  mas‐
       ter.cf name of the message delivery transport.

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_limit (default: $default_destination_concur‐
       rency_limit)
       A  transport-specific  override	for  the   default_destination_concur‐
       rency_limit  parameter  value, where transport is the master.cf name of
       the message delivery transport.

transport_destination_concurrency_negative_feedback (default:  $default_desti‐
       nation_concurrency_negative_feedback)
       A   transport-specific  override	 for  the  default_destination_concur‐
       rency_negative_feedback parameter value, where transport	 is  the  mas‐
       ter.cf name of the message delivery transport.

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_positive_feedback  (default: $default_desti‐
       nation_concurrency_positive_feedback)
       A  transport-specific  override	for  the   default_destination_concur‐
       rency_positive_feedback	parameter  value,  where transport is the mas‐
       ter.cf name of the message delivery transport.

       This feature is available in Postfix 2.5 and later.

transport_destination_rate_delay (default: $default_destination_rate_delay)
       A transport-specific override  for  the	default_destination_rate_delay
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

       This feature is available in Postfix 2.5 and later.

transport_destination_recipient_limit  (default:  $default_destination_recipi‐
       ent_limit)
       A   transport-specific  override	 for  the  default_destination_recipi‐
       ent_limit parameter value, where transport is the master.cf name of the
       message delivery transport.

transport_extra_recipient_limit (default: $default_extra_recipient_limit)
       A  transport-specific  override	for  the default_extra_recipient_limit
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

transport_initial_destination_concurrency  (default: $initial_destination_con‐
       currency)
       A transport-specific override for  the  initial_destination_concurrency
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

       This feature is available in Postfix 2.5 and later.

transport_maps (default: empty)
       Optional lookup tables with mappings from recipient address to (message
       delivery	  transport,  next-hop	destination).	See  transport(5)  for
       details.

       Specify zero or more "type:table" lookup tables.	 If you use this  fea‐
       ture  with  local files, run "postmap /usr/local/etc/postfix/transport"
       after making a change.

       For safety reasons, as of Postfix 2.3 this feature does not allow $num‐
       ber substitutions in regular expression maps.

       Examples:

       transport_maps = dbm:$config_directory/transport
       transport_maps = hash:$config_directory/transport

transport_minimum_delivery_slots (default: $default_minimum_delivery_slots)
       A  transport-specific  override	for the default_minimum_delivery_slots
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

transport_recipient_limit (default: $default_recipient_limit)
       A transport-specific override for the default_recipient_limit parameter
       value, where transport is the master.cf name of	the  message  delivery
       transport.

transport_recipient_refill_delay (default: $default_recipient_refill_delay)
       A  transport-specific  override	for the default_recipient_refill_delay
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       This feature is available in Postfix 2.4 and later.

transport_recipient_refill_limit (default: $default_recipient_refill_limit)
       A  transport-specific  override	for the default_recipient_refill_limit
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       This feature is available in Postfix 2.4 and later.

transport_retry_time (default: 60s)
       The  time  between  attempts  by the Postfix queue manager to contact a
       malfunctioning message delivery transport.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

transport_time_limit (default: $command_time_limit)
       A  transport-specific  override	for  the  command_time_limit parameter
       value, where transport is the master.cf name of	the  message  delivery
       transport.

trigger_timeout (default: 10s)
       The  time limit for sending a trigger to a Postfix daemon (for example,
       the pickup(8) or qmgr(8) daemon). This  time  limit  prevents  programs
       from getting stuck when the mail system is under heavy load.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

undisclosed_recipients_header (default: To: undisclosed-recipients:;)
       Message header that the Postfix cleanup(8) server inserts when  a  mes‐
       sage contains no To: or Cc: message header. With Postfix 2.4 and later,
       specify an empty value to disable this feature.

unknown_address_reject_code (default: 450)
       The numerical Postfix SMTP server response code when a sender or recip‐
       ient   address  is  rejected  by	 the  reject_unknown_sender_domain  or
       reject_unknown_recipient_domain restriction.  The  response  is	always
       450 in case of a temporary DNS error.

       Do  not	change	this  unless  you have a complete understanding of RFC
       2821.

unknown_address_tempfail_action (default: $reject_tempfail_action)
       The Postfix SMTP server's action when  reject_unknown_sender_domain  or
       reject_unknown_recipient_domain	fail  due  to a temporary error condi‐
       tion. Specify "defer" to defer the remote SMTP client  request  immedi‐
       ately.  With  the  default  "defer_if_permit"  action, the Postfix SMTP
       server continues to look for opportunities to reject mail,  and	defers
       the client request only if it would otherwise be accepted.

       This feature is available in Postfix 2.6 and later.

unknown_client_reject_code (default: 450)
       The  numerical  Postfix SMTP server response code when a client without
       valid   address	 <=>	name	mapping	   is	 rejected    by	   the
       reject_unknown_client_hostname  restriction.  The  SMTP	server	always
       replies with 450 when the mapping failed due to a temporary error  con‐
       dition.

       Do  not	change	this  unless  you have a complete understanding of RFC
       2821.

unknown_helo_hostname_tempfail_action (default: $reject_tempfail_action)
       The Postfix  SMTP  server's  action  when  reject_unknown_helo_hostname
       fails due to an temporary error condition. Specify "defer" to defer the
       remote SMTP client request immediately. With the default "defer_if_per‐
       mit"  action,  the Postfix SMTP server continues to look for opportuni‐
       ties to reject mail, and defers the client request  only	 if  it	 would
       otherwise be accepted.

       This feature is available in Postfix 2.6 and later.

unknown_hostname_reject_code (default: 450)
       The numerical Postfix SMTP server response code when the hostname spec‐
       ified  with  the	 HELO	or   EHLO   command   is   rejected   by   the
       reject_unknown_helo_hostname restriction.

       Do  not	change	this  unless  you have a complete understanding of RFC
       2821.

unknown_local_recipient_reject_code (default: 550)
       The numerical Postfix  SMTP  server  response  code  when  a  recipient
       address	is local, and $local_recipient_maps specifies a list of lookup
       tables that does not match the recipient.  A recipient address is local
       when   its   domain   matches   $mydestination,	 $proxy_interfaces  or
       $inet_interfaces.

       The default setting is 550 (reject mail) but it is safer	 to  initially
       use  450	 (try  again  later)  so  you  have  time  to find out if your
       local_recipient_maps settings are OK.

       Example:

       unknown_local_recipient_reject_code = 450

       This feature is available in Postfix 2.0 and later.

unknown_relay_recipient_reject_code (default: 550)
       The numerical Postfix SMTP server reply code when a  recipient  address
       matches	$relay_domains,	 and  relay_recipient_maps specifies a list of
       lookup tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_alias_reject_code (default: 550)
       The SMTP server reply code  when	 a  recipient  address	matches	 $vir‐
       tual_alias_domains,  and $virtual_alias_maps specifies a list of lookup
       tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_mailbox_reject_code (default: 550)
       The SMTP server reply code  when	 a  recipient  address	matches	 $vir‐
       tual_mailbox_domains,  and  $virtual_mailbox_maps  specifies  a list of
       lookup tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unverified_recipient_defer_code (default: 450)
       The numerical Postfix SMTP server response  when	 a  recipient  address
       probe fails due to a temporary error condition.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do not change this unless you have  a  complete	understanding  of  RFC
       2821.

       This feature is available in Postfix 2.6 and later.

unverified_recipient_reject_code (default: 450)
       The  numerical Postfix SMTP server response when a recipient address is
       rejected by the reject_unverified_recipient restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do  not	change	this  unless  you have a complete understanding of RFC
       2821.

       This feature is available in Postfix 2.1 and later.

unverified_recipient_reject_reason (default: empty)
       The Postfix SMTP server's reply when rejecting mail with reject_unveri‐
       fied_recipient.	Do  not	 include  the  numeric	SMTP reply code or the
       enhanced status code. By default, the response includes actual  address
       verification details.

       Example:

       unverified_recipient_reject_reason = Recipient address lookup failed

       This feature is available in Postfix 2.6 and later.

unverified_recipient_tempfail_action (default: $reject_tempfail_action)
       The Postfix SMTP server's action when reject_unverified_recipient fails
       due to a temporary error condition. Specify "defer" to defer the remote
       SMTP  client  request  immediately.  With the default "defer_if_permit"
       action, the Postfix SMTP server continues to look for opportunities  to
       reject  mail,  and defers the client request only if it would otherwise
       be accepted.

       This feature is available in Postfix 2.6 and later.

unverified_sender_defer_code (default: 450)
       The numerical Postfix SMTP server response code when a  sender  address
       probe fails due to a temporary error condition.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do not change this unless you have  a  complete	understanding  of  RFC
       2821.

       This feature is available in Postfix 2.6 and later.

unverified_sender_reject_code (default: 450)
       The  numerical  Postfix	SMTP  server  response	code  when a recipient
       address is rejected by the reject_unverified_sender restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do  not	change	this  unless  you have a complete understanding of RFC
       2821.

       This feature is available in Postfix 2.1 and later.

unverified_sender_reject_reason (default: empty)
       The Postfix SMTP server's reply when rejecting mail with reject_unveri‐
       fied_sender. Do not include the numeric SMTP reply code or the enhanced
       status code. By default, the response includes actual address verifica‐
       tion details.

       Example:

       unverified_sender_reject_reason = Sender address lookup failed

       This feature is available in Postfix 2.6 and later.

unverified_sender_tempfail_action (default: $reject_tempfail_action)
       The  Postfix  SMTP  server's action when reject_unverified_sender fails
       due to a temporary error condition. Specify "defer" to defer the remote
       SMTP  client  request  immediately.  With the default "defer_if_permit"
       action, the Postfix SMTP server continues to look for opportunities  to
       reject  mail,  and defers the client request only if it would otherwise
       be accepted.

       This feature is available in Postfix 2.6 and later.

verp_delimiter_filter (default: -=+)
       The characters Postfix accepts as  VERP	delimiter  characters  on  the
       Postfix sendmail(1) command line and in SMTP commands.

       This feature is available in Postfix 1.1 and later.

virtual_alias_domains (default: $virtual_alias_maps)
       Postfix	is  final  destination for the specified list of virtual alias
       domains, that is, domains  for  which  all  addresses  are  aliased  to
       addresses  in  other local or remote domains. The SMTP server validates
       recipient addresses with $virtual_alias_maps and	 rejects  non-existent
       recipients.   See   also	  the	virtual	 alias	domain	class  in  the
       ADDRESS_CLASS_README file

       This feature is available in Postfix 2.0 and later. The	default	 value
       is backwards compatible with Postfix version 1.1.

       The  default  value  is	$virtual_alias_maps  so	 that you can keep all
       information about virtual alias domains in one place.  If you have many
       users,  it  is  better  to  separate information that changes more fre‐
       quently (virtual address ->  local  or  remote  address	mapping)  from
       information  that  changes  less frequently (the list of virtual domain
       names).

       Specify a list of host or domain names,	"/file/name"  or  "type:table"
       patterns, separated by commas and/or whitespace. A "/file/name" pattern
       is replaced by its contents; a "type:table"  lookup  table  is  matched
       when  a	table  entry  matches  a  lookup  string (the lookup result is
       ignored).  Continue long lines by starting the next  line  with	white‐
       space.  Specify	"!pattern"  to	exclude a host or domain name from the
       list. The form "!/file/name" is supported only in Postfix  version  2.4
       and later.

       See also the VIRTUAL_README and ADDRESS_CLASS_README documents for fur‐
       ther information.

       Example:

       virtual_alias_domains = virtual1.tld virtual2.tld

virtual_alias_expansion_limit (default: 1000)
       The maximal number of addresses that virtual alias  expansion  produces
       from each original recipient.

       This feature is available in Postfix 2.1 and later.

virtual_alias_maps (default: $virtual_maps)
       Optional lookup tables that alias specific mail addresses or domains to
       other local or remote address.  The table format and lookups are	 docu‐
       mented  in virtual(5). For an overview of Postfix address manipulations
       see the ADDRESS_REWRITING_README document.

       This feature is available in Postfix 2.0 and later. The	default	 value
       is backwards compatible with Postfix version 1.1.

       If   you	  use	this   feature	 with	indexed	 files,	 run  "postmap
       /usr/local/etc/postfix/virtual" after changing the file.

       Examples:

       virtual_alias_maps = dbm:$config_directory/virtual
       virtual_alias_maps = hash:$config_directory/virtual

virtual_alias_recursion_limit (default: 1000)
       The maximal nesting depth of virtual alias  expansion.	Currently  the
       recursion  limit	 is  applied  only to the left branch of the expansion
       graph, so the depth of the tree can in the worst case reach the sum  of
       the expansion and recursion limits.  This may change in the future.

       This feature is available in Postfix 2.1 and later.

virtual_destination_concurrency_limit  (default:  $default_destination_concur‐
       rency_limit)
       The maximal number of parallel deliveries to the same  destination  via
       the  virtual  message delivery transport. This limit is enforced by the
       queue manager. The message delivery transport name is the  first	 field
       in the entry in the master.cf file.

virtual_destination_recipient_limit   (default:	  $default_destination_recipi‐
       ent_limit)
       The maximal number of recipients per message for	 the  virtual  message
       delivery	 transport.  This  limit is enforced by the queue manager. The
       message delivery transport name is the first field in the entry in  the
       master.cf file.

       Setting	this  parameter	 to  a	value of 1 changes the meaning of vir‐
       tual_destination_concurrency_limit from	concurrency  per  domain  into
       concurrency per recipient.

virtual_gid_maps (default: empty)
       Lookup  tables  with  the per-recipient group ID for virtual(8) mailbox
       delivery.

       In a lookup table, specify a left-hand side of "@domain.tld"  to	 match
       any  user  in  the  specified  domain  that  does  not  have a specific
       "user@domain.tld" entry.

       When  a	recipient  address   has   an	optional   address   extension
       (user+foo@domain.tld),  the virtual(8) delivery agent looks up the full
       address first, and when the lookup fails, it looks  up  the  unextended
       address (user@domain.tld).

       Note  1:	 for security reasons, the virtual(8) delivery agent disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note  2:	 for  security	reasons,  the  virtual(8)  delivery agent will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open  the  table	 directly.  Before Postfix version 2.2, the virtual(8)
       delivery agent will terminate with a fatal error.

virtual_mailbox_base (default: empty)
       A prefix that the virtual(8) delivery agent prepends  to	 all  pathname
       results	from  $virtual_mailbox_maps  table  lookups.  This is a safety
       measure to ensure that an out of control map doesn't  litter  the  file
       system with mailboxes.  While virtual_mailbox_base could be set to "/",
       this setting isn't recommended.

       Example:

       virtual_mailbox_base = /var/mail

virtual_mailbox_domains (default: $virtual_mailbox_maps)
       Postfix is final destination for the specified list of domains; mail is
       delivered  via  the  $virtual_transport	mail  delivery	transport.  By
       default this is the Postfix virtual(8) delivery agent.  The SMTP server
       validates  recipient  addresses	with $virtual_mailbox_maps and rejects
       mail for non-existent recipients.  See also the virtual mailbox	domain
       class in the ADDRESS_CLASS_README file.

       This  parameter expects the same syntax as the mydestination configura‐
       tion parameter.

       This feature is available in Postfix 2.0 and later. The	default	 value
       is backwards compatible with Postfix version 1.1.

virtual_mailbox_limit (default: 51200000)
       The  maximal  size  in  bytes  of  an  individual virtual(8) mailbox or
       maildir file, or zero (no limit).

virtual_mailbox_lock (default: see postconf -d output)
       How to lock a UNIX-style virtual(8) mailbox before attempting delivery.
       For  a  list  of	 available file locking methods, use the "postconf -l"
       command.

       This setting is ignored	with  maildir  style  delivery,	 because  such
       deliveries are safe without application-level locks.

       Note  1:	 the dotlock method requires that the recipient UID or GID has
       write access to the parent directory of the recipient's mailbox file.

       Note 2: the default setting of this parameter is system dependent.

virtual_mailbox_maps (default: empty)
       Optional lookup tables with all valid addresses	in  the	 domains  that
       match $virtual_mailbox_domains.

       In  a  lookup table, specify a left-hand side of "@domain.tld" to match
       any user in  the	 specified  domain  that  does	not  have  a  specific
       "user@domain.tld" entry.

       The virtual(8) delivery agent uses this table to look up the per-recip‐
       ient mailbox or maildir pathname.  If the lookup result ends in a slash
       ("/"),  maildir-style  delivery	is  carried out, otherwise the path is
       assumed to specify a UNIX-style mailbox file.  Note that $virtual_mail‐
       box_base is unconditionally prepended to this path.

       When   a	  recipient   address	has   an  optional  address  extension
       (user+foo@domain.tld), the virtual(8) delivery agent looks up the  full
       address	first,	and  when the lookup fails, it looks up the unextended
       address (user@domain.tld).

       Note 1: for security reasons, the virtual(8) delivery  agent  disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note 2: for  security  reasons,	the  virtual(8)	 delivery  agent  will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open the table directly. Before Postfix	version	 2.2,  the  virtual(8)
       delivery agent will terminate with a fatal error.

virtual_maps (default: empty)
       Optional lookup tables with a) names of domains for which all addresses
       are aliased to addresses in other  local	 or  remote  domains,  and  b)
       addresses  that	are  aliased  to  addresses  in	 other local or remote
       domains.	 Available before Postfix version 2.0.	With  Postfix  version
       2.0   and   later,   this   is  replaced	 by  separate  controls:  vir‐
       tual_alias_domains and virtual_alias_maps.

virtual_minimum_uid (default: 100)
       The minimum user ID value that the virtual(8) delivery agent accepts as
       a  result  from	$virtual_uid_maps  table lookup.  Returned values less
       than this will be rejected, and the message will be deferred.

virtual_transport (default: virtual)
       The default mail delivery transport and next-hop destination for	 final
       delivery	 to domains listed with $virtual_mailbox_domains.  This infor‐
       mation can be overruled with the transport(5) table.

       Specify a string of the form transport:nexthop, where transport is  the
       name  of	 a mail delivery transport defined in master.cf.  The :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       This feature is available in Postfix 2.0 and later.

virtual_uid_maps (default: empty)
       Lookup tables with the per-recipient user ID that the virtual(8) deliv‐
       ery agent uses while writing to the recipient's mailbox.

       In a lookup table, specify a left-hand side of "@domain.tld"  to	 match
       any  user  in  the  specified  domain  that  does  not  have a specific
       "user@domain.tld" entry.

       When  a	recipient  address   has   an	optional   address   extension
       (user+foo@domain.tld),  the virtual(8) delivery agent looks up the full
       address first, and when the lookup fails, it looks  up  the  unextended
       address (user@domain.tld).

       Note  1:	 for security reasons, the virtual(8) delivery agent disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note  2:	 for  security	reasons,  the  virtual(8)  delivery agent will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open  the  table	 directly.  Before Postfix version 2.2, the virtual(8)
       delivery agent will terminate with a fatal error.

SEE ALSO
       postconf(1), Postfix configuration parameter maintenance
       master(5), Postfix daemon configuration maintenance

LICENSE
       The Secure Mailer license must be distributed with this software.

AUTHOR(S)
       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

								   POSTCONF(5)
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