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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
       discarded.  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
              maintained 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
              message 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
              destination.

       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
              doubled after each attempt.

       destination status cache
              The queue manager avoids unnecessary delivery attempts by
              maintaining a short-term, in-memory list of unreachable
              destinations.

       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
       message.  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
       outside 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
       postmaster is notified of bounces and of other trouble.

BUGS
       A single queue manager process has to compete for disk access with
       multiple 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
       persistent 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_concurrency_limit)
              Idem, for delivery via the named message transport.

       Available in Postfix version 2.5 and later:

       transport_initial_destination_concurrency
              ($initial_destination_concurrency)
              Initial concurrency for delivery via the named message
              transport.

       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_destination_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
              handshake failure.

       transport_destination_concurrency_negative_feedback
              ($default_destination_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
              handshake failure.

       transport_destination_concurrency_positive_feedback
              ($default_destination_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
              performance 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_recipient_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
              contact 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
              considered 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
              recipient 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
              information over an internal communication channel.

MISCELLANEOUS CONTROLS

       config_directory (see 'postconf -d' output)
              The default location of the Postfix main.cf and master.cf
              configuration 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
              logging sub-second delay values.

       helpful_warnings (yes)
              Log warnings about problematic configuration settings, and
              provide 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,
              "postfix/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)