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QMGR(8)								       QMGR(8)

NAME
       qmgr - Postfix queue manager

SYNOPSIS
       qmgr [generic Postfix daemon options]

DESCRIPTION
       The qmgr(8) daemon awaits the arrival of incoming mail and arranges for
       its delivery via Postfix delivery processes.  The actual	 mail  routing
       strategy	 is  delegated to the trivial-rewrite(8) daemon.  This program
       expects to be run from the master(8) process manager.

       Mail addressed to the local double-bounce address is  logged  and  dis‐
       carded.	 This  stops  potential	 loops	caused by undeliverable bounce
       notifications.

MAIL QUEUES
       The qmgr(8) daemon maintains the following queues:

       incoming
	      Inbound mail from the network, or mail picked up	by  the	 local
	      pickup(8) daemon from the maildrop directory.

       active Messages	that the queue manager has opened for delivery. Only a
	      limited number of messages is allowed to enter the active	 queue
	      (leaky bucket strategy, for a fixed delivery rate).

       deferred
	      Mail  that  could	 not  be delivered upon the first attempt. The
	      queue manager implements exponential  backoff  by	 doubling  the
	      time between delivery attempts.

       corrupt
	      Unreadable or damaged queue files are moved here for inspection.

       hold   Messages	that  are  kept	 "on hold" are kept here until someone
	      sets them free.

DELIVERY STATUS REPORTS
       The qmgr(8) daemon keeps an eye on per-message delivery status  reports
       in the following directories. Each status report file has the same name
       as the corresponding message file:

       bounce Per-recipient status information	about  why  mail  is  bounced.
	      These files are maintained by the bounce(8) daemon.

       defer  Per-recipient  status  information  about	 why  mail is delayed.
	      These files are maintained by the defer(8) daemon.

       trace  Per-recipient status information as requested with  the  Postfix
	      "sendmail	 -v" or "sendmail -bv" command.	 These files are main‐
	      tained by the trace(8) daemon.

       The qmgr(8) daemon is responsible for asking the bounce(8), defer(8) or
       trace(8) daemons to send delivery reports.

STRATEGIES
       The queue manager implements a variety of strategies for either opening
       queue files (input) or for message delivery (output).

       leaky bucket
	      This strategy limits the number of messages in the active	 queue
	      and  prevents the queue manager from running out of memory under
	      heavy load.

       fairness
	      When the active queue has room, the queue manager takes one mes‐
	      sage  from  the  incoming queue and one from the deferred queue.
	      This prevents a large mail backlog from blocking the delivery of
	      new mail.

       slow start
	      This  strategy  eliminates  "thundering herd" problems by slowly
	      adjusting the number of parallel deliveries to the same destina‐
	      tion.

       round robin
	      The  queue  manager  sorts  delivery  requests  by  destination.
	      Round-robin selection prevents one destination  from  dominating
	      deliveries to other destinations.

       exponential backoff
	      Mail  that  cannot  be  delivered	 upon  the  first  attempt  is
	      deferred.	 The time interval between delivery attempts  is  dou‐
	      bled after each attempt.

       destination status cache
	      The  queue manager avoids unnecessary delivery attempts by main‐
	      taining a short-term, in-memory  list  of	 unreachable  destina‐
	      tions.

       preemptive message scheduling
	      The queue manager attempts to minimize the average per-recipient
	      delay while still preserving  the	 correct  per-message  delays,
	      using a sophisticated preemptive message scheduling.

TRIGGERS
       On  an  idle system, the queue manager waits for the arrival of trigger
       events, or it waits for a timer to go off. A trigger is a one-byte mes‐
       sage.   Depending  on  the message received, the queue manager performs
       one of the following actions (the message is followed by	 the  symbolic
       constant used internally by the software):

       D (QMGR_REQ_SCAN_DEFERRED)
	      Start  a	deferred  queue	 scan.	 If  a	deferred queue scan is
	      already in progress, that scan will be restarted as soon	as  it
	      finishes.

       I (QMGR_REQ_SCAN_INCOMING)
	      Start  an	 incoming  queue  scan.	 If  an incoming queue scan is
	      already in progress, that scan will be restarted as soon	as  it
	      finishes.

       A (QMGR_REQ_SCAN_ALL)
	      Ignore  deferred queue file time stamps. The request affects the
	      next deferred queue scan.

       F (QMGR_REQ_FLUSH_DEAD)
	      Purge all information about dead transports and destinations.

       W (TRIGGER_REQ_WAKEUP)
	      Wakeup call, This is used by the master  server  to  instantiate
	      servers  that should not go away forever. The action is to start
	      an incoming queue scan.

       The qmgr(8) daemon reads an entire buffer worth of triggers.   Multiple
       identical trigger requests are collapsed into one, and trigger requests
       are sorted so that A and F precede D and I. Thus, in order to  force  a
       deferred	 queue	run,  one  would request A F D; in order to notify the
       queue manager of the arrival of new mail one would request I.

STANDARDS
       RFC 3463 (Enhanced status codes)
       RFC 3464 (Delivery status notifications)

SECURITY
       The qmgr(8) daemon is not security sensitive. It reads single-character
       messages	 from  untrusted  local	 users, and thus may be susceptible to
       denial of service attacks. The qmgr(8) daemon does not talk to the out‐
       side  world,  and  it  can  be run at fixed low privilege in a chrooted
       environment.

DIAGNOSTICS
       Problems and transactions are logged to the syslog  daemon.   Corrupted
       message files are saved to the corrupt queue for further inspection.

       Depending  on the setting of the notify_classes parameter, the postmas‐
       ter is notified of bounces and of other trouble.

BUGS
       A single queue manager process has to compete for disk access with mul‐
       tiple front-end processes such as cleanup(8). A sudden burst of inbound
       mail can negatively impact outbound delivery rates.

CONFIGURATION PARAMETERS
       Changes to main.cf are not picked up automatically as qmgr(8) is a per‐
       sistent process. Use the "postfix reload" command after a configuration
       change.

       The text below provides only a parameter summary. See  postconf(5)  for
       more details including examples.

       In the text below, transport is the first field in a master.cf entry.

COMPATIBILITY CONTROLS
       Available before Postfix version 2.5:

       allow_min_user (no)
	      Allow  a	sender	or  recipient address to have `-' as the first
	      character.

       Available with Postfix version 2.7 and later:

       default_filter_nexthop (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.

ACTIVE QUEUE CONTROLS
       qmgr_clog_warn_time (300s)
	      The minimal delay between warnings that a	 specific  destination
	      is clogging up the Postfix active queue.

       qmgr_message_active_limit (20000)
	      The maximal number of messages in the active queue.

       qmgr_message_recipient_limit (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 (10)
	      The minimal number of in-memory recipients for any message.

       default_recipient_limit (20000)
	      The default per-transport upper limit on the number of in-memory
	      recipients.

       transport_recipient_limit ($default_recipient_limit)
	      Idem, for delivery via the named message transport.

       default_extra_recipient_limit (1000)
	      The default value for the extra per-transport limit  imposed  on
	      the number of in-memory recipients.

       transport_extra_recipient_limit ($default_extra_recipient_limit)
	      Idem, for delivery via the named message transport.

       Available in Postfix version 2.4 and later:

       default_recipient_refill_limit (100)
	      The  default  per-transport  limit  on  the number of recipients
	      refilled at once.

       transport_recipient_refill_limit ($default_recipient_refill_limit)
	      Idem, for delivery via the named message transport.

       default_recipient_refill_delay (5s)
	      The  default  per-transport  maximum  delay  between  recipients
	      refills.

       transport_recipient_refill_delay ($default_recipient_refill_delay)
	      Idem, for delivery via the named message transport.

DELIVERY CONCURRENCY CONTROLS
       initial_destination_concurrency (5)
	      The  initial  per-destination  concurrency  level	 for  parallel
	      delivery to the same destination.

       default_destination_concurrency_limit (20)
	      The default maximal number of parallel deliveries	 to  the  same
	      destination.

       transport_destination_concurrency_limit	 ($default_destination_concur‐
       rency_limit)
	      Idem, for delivery via the named message transport.

       Available in Postfix version 2.5 and later:

       transport_initial_destination_concurrency ($initial_destination_concur‐
       rency)
	      Initial  concurrency  for	 delivery via the named message trans‐
	      port.

       default_destination_concurrency_failed_cohort_limit (1)
	      How many pseudo-cohorts  must  suffer  connection	 or  handshake
	      failure  before a specific destination is considered unavailable
	      (and further delivery is suspended).

       transport_destination_concurrency_failed_cohort_limit  ($default_desti‐
       nation_concurrency_failed_cohort_limit)
	      Idem, for delivery via the named message transport.

       default_destination_concurrency_negative_feedback (1)
	      The  per-destination  amount  of	delivery  concurrency negative
	      feedback, after a delivery completes with a connection or	 hand‐
	      shake failure.

       transport_destination_concurrency_negative_feedback  ($default_destina‐
       tion_concurrency_negative_feedback)
	      Idem, for delivery via the named message transport.

       default_destination_concurrency_positive_feedback (1)
	      The per-destination  amount  of  delivery	 concurrency  positive
	      feedback, after a delivery completes without connection or hand‐
	      shake failure.

       transport_destination_concurrency_positive_feedback  ($default_destina‐
       tion_concurrency_positive_feedback)
	      Idem, for delivery via the named message transport.

       destination_concurrency_feedback_debug (no)
	      Make  the queue manager's feedback algorithm verbose for perfor‐
	      mance analysis purposes.

RECIPIENT SCHEDULING CONTROLS
       default_destination_recipient_limit (50)
	      The default maximal number of recipients per message delivery.

       transport_destination_recipient_limit	 ($default_destination_recipi‐
       ent_limit)
	      Idem, for delivery via the named message transport.

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

       transport_delivery_slot_cost ($default_delivery_slot_cost)
	      Idem, for delivery via the named message transport.

       default_minimum_delivery_slots (3)
	      How many recipients a message must have in order to  invoke  the
	      Postfix queue manager's scheduling algorithm at all.

       transport_minimum_delivery_slots ($default_minimum_delivery_slots)
	      Idem, for delivery via the named message transport.

       default_delivery_slot_discount (50)
	      The default value for transport-specific _delivery_slot_discount
	      settings.

       transport_delivery_slot_discount ($default_delivery_slot_discount)
	      Idem, for delivery via the named message transport.

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

       transport_delivery_slot_loan ($default_delivery_slot_loan)
	      Idem, for delivery via the named message transport.

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

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

       maximal_queue_lifetime (5d)
	      The maximal time a message is queued before it is sent  back  as
	      undeliverable.

       queue_run_delay (300s)
	      The  time	 between  deferred  queue  scans by the queue manager;
	      prior to Postfix 2.4 the default value was 1000s.

       transport_retry_time (60s)
	      The time between attempts by the Postfix queue manager  to  con‐
	      tact a malfunctioning message delivery transport.

       Available in Postfix version 2.1 and later:

       bounce_queue_lifetime (5d)
	      The maximal time a bounce message is queued before it is consid‐
	      ered undeliverable.

       Available in Postfix version 2.5 and later:

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

       transport_destination_rate_delay $default_destination_rate_delay
	      Idem, for delivery via the named message transport.

SAFETY CONTROLS
       qmgr_daemon_timeout (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.

       qmgr_ipc_timeout (60s)
	      The time limit for the queue manager to send or receive informa‐
	      tion over an internal communication channel.

MISCELLANEOUS CONTROLS
       config_directory (see 'postconf -d' output)
	      The  default  location of the Postfix main.cf and master.cf con‐
	      figuration files.

       defer_transports (empty)
	      The names of message delivery transports that should not deliver
	      mail unless someone issues "sendmail -q" or equivalent.

       delay_logging_resolution_limit (2)
	      The  maximal  number of digits after the decimal point when log‐
	      ging sub-second delay values.

       helpful_warnings (yes)
	      Log warnings about problematic configuration settings, and  pro‐
	      vide helpful suggestions.

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

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

       queue_directory (see 'postconf -d' output)
	      The location of the Postfix top-level queue directory.

       syslog_facility (mail)
	      The syslog facility of Postfix logging.

       syslog_name (see 'postconf -d' output)
	      The  mail	 system	 name that is prepended to the process name in
	      syslog records, so that "smtpd"  becomes,	 for  example,	"post‐
	      fix/smtpd".

FILES
       /var/spool/postfix/incoming, incoming queue
       /var/spool/postfix/active, active queue
       /var/spool/postfix/deferred, deferred queue
       /var/spool/postfix/bounce, non-delivery status
       /var/spool/postfix/defer, non-delivery status
       /var/spool/postfix/trace, delivery status

SEE ALSO
       trivial-rewrite(8), address routing
       bounce(8), delivery status reports
       postconf(5), configuration parameters
       master(5), generic daemon options
       master(8), process manager
       syslogd(8), system logging

README FILES
       Use  "postconf readme_directory" or "postconf html_directory" to locate
       this information.
       SCHEDULER_README, scheduling algorithm
       QSHAPE_README, Postfix queue analysis

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

       Preemptive scheduler enhancements:
       Patrik Rak
       Modra 6
       155 00, Prague, Czech Republic

								       QMGR(8)
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