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QMGR(8)			    System Manager's Manual		       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 no-
       tifications.

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 de-
	      ferred.  The time	interval between delivery attempts is  doubled
	      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, us-
	      ing 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 al-
	      ready 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 al-
	      ready 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 de-
       nial 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 en-
       vironment.

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 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 re-
	      filled 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  re-
	      fills.

       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 de-
	      livery 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)
	      Consider a message as undeliverable, when	delivery fails with  a
	      temporary	error, and the time in the queue has reached the maxi-
	      mal_queue_lifetime limit.

       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)
	      Consider a bounce	message	as undeliverable, when delivery	 fails
	      with  a  temporary  error, and the time in the queue has reached
	      the bounce_queue_lifetime	limit.

       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; the	resulting behavior de-
	      pends on the value of the	corresponding per-destination  recipi-
	      ent limit.

       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)

NAME | SYNOPSIS | DESCRIPTION | MAIL QUEUES | DELIVERY STATUS REPORTS | STRATEGIES | TRIGGERS | STANDARDS | SECURITY | DIAGNOSTICS | BUGS | CONFIGURATION PARAMETERS | COMPATIBILITY CONTROLS | ACTIVE QUEUE CONTROLS | DELIVERY CONCURRENCY CONTROLS | RECIPIENT SCHEDULING CONTROLS | MESSAGE SCHEDULING CONTROLS | OTHER RESOURCE AND RATE CONTROLS | SAFETY CONTROLS | MISCELLANEOUS CONTROLS | FILES | SEE ALSO | README FILES | LICENSE | AUTHOR(S)

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