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SMTPD(6)							      SMTPD(6)

       smtpd - SMTP listener configuration

       The SMTP daemon of mail(1) implements the slave side of the SMTP proto‐
       col to accept incoming mail  on	TCP  port  25.	 In  general,  smtpd's
       default	parameters  are	 sufficient  for internal systems on protected
       networks, but external or gateway systems require  additional  security
       mechanisms.   The  files /mail/lib/smtpd.conf, containing configuration
       parameters, and /mail/lib/blocked, containing banished addresses,  pro‐
       vide the means to exercise these facilities.

   Input Format
       In  both	 files	input  lines consist of a verb followed by one or more
       parameters.  These tokens are separated by white space  or  commas  and
       all  characters	following  a  #	 are comments.	A # cannot be escaped.
       Continuation lines are not supported,  but  verbs  that	take  multiple
       parameters  can be restated on many lines and the associated parameters
       accumulate into a single set.  All token	 processing  is	 case-insensi‐

       Many  parameters	 are  addresses,  either  numeric IP addresses in CIDR
       notation or a sender address in UUCP-style format.

       An IP address in CIDR notation has the form


       consisting of a four octet IP address, a slash, and a mask length spec‐
       ifying  the  number of significant high-order bits.  The lower the mask
       length, the larger the range of addresses covered by the CIDR  address;
       see  RFC	 1878  for  a  discussion  of mask lengths.  Missing low-order
       octets are assumed to be zero.  If a mask length is not given,  a  mask
       length of 16, 24, or 32 is assumed for addresses containing two, three,
       or four octets, respectively.  These mask lengths  select  a  class  B,
       class  C or Class D address block.  Notice that this convention differs
       from the standard treatment, where the default mask length  depends  on
       the allocation class of the network block containing the address.

       Sender addresses are specified in UUCP notation as follows:


       It is seldom necessary to specify more than one domain.	When domain is
       missing or *, the address selects the specified user in all domains.  A
       domain  of  the	form  *.domain	selects the domain and all of its sub-
       domains.	 For example,!user only matches the	 account  user
       in domain, while *!user selects that account in and all of its sub-domains.	When user is omitted or *, the
       address	selects all users in the specified domain.  Finally, when * is
       the last character of the user name it is a wild-card matching all user
       names  beginning	 with  user.  This limited pattern matching capability
       should be used with care.  For safety, the sender addresses *,  !,  *!,
       !*  and *!*  are ignored.

       This  file contains configuration options and parameters describing the
       local domain.  Many of the options can also be specified on the command
       line;  command  line  options  always override the values in this file.
       Configuration options are:

       defaultdomain domain
		 The name of the local domain; it  is  appended	 to  addresses
		 lacking  a domain qualification.  This is identical to the -h
		 command line option.

       norelay [on|off]
		 If on is specified, relaying is prohibited from  unauthorized
		 networks   to	external  domains.   Authorized	 networks  and
		 domains must be specified by the ournets and ourdomains verbs
		 described  below.   Setting  this  option on is equivalent to
		 specifying the -f command line flag, but the list of networks
		 and domains can only be specified in this file.

       verifysenderdom [on|off]
		 When on, smtpd verifies that the first domain of the sender's
		 address exists.  The test is cursory;	it  checks  only  that
		 there is a DNS delegation for the domain.  Setting the option
		 on is equivalent to specifying the -r command line option and
		 is useful for detecting some unreturnable messages as well as
		 messages with randomly generated domain names.

       saveblockedmsg [on|off]
		 When on, causes copies of blocked messages  to	 be  saved  in
		 subdirectories	 of  /mail/queue.dump.	 Directories are named
		 with the date and file names are  random  numbers.   If  this
		 option	 is  off blocked messages are discarded.  Setting this
		 option on is equivalent to specifying	the  -s	 command  line

       ournets IP address [, IP address, ..., IP address]
		 This  option  specifies  trusted  source  networks  that  are
		 allowed to relay mail to external domains.  These are usually
		 the  internal networks of the local domain, but they can also
		 include friendly external networks.  Addresses	 are  in  CIDR

       ourdomains domain [, domain, ..., domain]
		 This option specifies destination domains that are allowed to
		 receive relayed mail.	These are usually the  domains	served
		 by  a	gateway	 system.  Domain specifications conform to the
		 format for sender addresses given above.

       When the norelay option is enabled or the -f command line option given,
       relaying	 is allowed only if the source IP address is in ournets or the
       destination domain is specified in ourdomains.

   Blocked Addresses
       Smtpd consults  /mail/ratify  (see  ratfs(4))  for  a  list  of	banned
       addresses.   Messages received from these addresses are rejected with a
       5xx-series SMTP error code.  There is no option to turn blocking on  or
       off;  if	 /mail/ratify  is mounted, smtpd will use it, even for connec‐
       tions from trusted networks.

       The command line format and address specifications conform to the nota‐
       tion  described	above.	 If  the  parameters  of  the  verb  is sender
       addresses in UUCP format, the line must begin with an *	character;  if
       the  parameters	are  one  or more IP addresses, the * must precede the
       verb.  Most verbs cause messages to be rejected; verbs  of  this	 class
       generally select different error messages.  The remaining verbs specify
       addresses that  are  always  accepted,  in  effect  overriding  blocked
       addresses.  The file is processed in order, so an override must precede
       its associated blocked address.	Supported verbs are:

       dial IP address [,..., IP address]
		 The parameters	 are  IP  addresses  associated	 with  dial-up
		 ports.	  The  rejection  message states that connections from
		 dial-up ports are not accepted.  Copies of messages are never

       block address [, ... address]
		 Messages  from addresses matching the parameters are rejected
		 with an error message saying that spam is not accepted.   The
		 message is saved if the option is enabled.

       relay address [, ... address]
		 This verb is identical to block, but the error message states
		 that the message is rejected because the  sending  system  is
		 being used as a spam relay.

       deny address [, ... address]
		 The  deny  command  rejects a message when the sender address
		 matches one of its parameters.	 The  rejection	 message  asks
		 the  sender  to  contact  postmaster@	hostdomain for further
		 information.  This verb is usually  used  to  block  inadver‐
		 tently	 abusive  traffic,  for	 example, mail loops and stuck
		 senders.  Messages are never saved.

       allow address [, ... address]
		 The allow verb negates the effect of subsequent blocking com‐
		 mands.	 It is useful when a large range of addresses contains
		 a few legitimate addresses, for example, when a  mail	server
		 is  in	 a  Class C network block of modem ports.  Rather than
		 enumerate the dial ports, it is easier to  block  the	entire
		 Class	C with a dial command, and precede it with an override
		 for the address of the mail server.  Similarly, it is	possi‐
		 ble  to block mail from an entire domain while accepting mail
		 from a few friendly senders in the domain.  The  verb	accept
		 is a synonym for allow.

       Scanmail(8)  describes spam detection software that works well with the
       capabilities described here and mail(1) defines additional  smtpd  com‐
       mand line arguments applicable to exposed systems.

       mail(1), ratfs(4), scanmail(8)

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