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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:



  

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

  

  
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).

  

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

  

  
Unreadable or damaged queue files are moved here for inspection.

  

  
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:



  

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

  

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

  

  
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).



  

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

  

  
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.

  

  
This strategy eliminates "thundering herd" problems by slowly
      adjusting the number of parallel deliveries to the same destination.

  

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

  

  
Mail that cannot be delivered upon the first attempt is deferred. The time
      interval between delivery attempts is doubled after each attempt.

  

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

  

  
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):



  

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

  

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

  

  
Ignore deferred queue file time stamps. The request affects the next
      deferred queue scan.

  

  
Purge all information about dead transports and destinations.

  

  
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 syslogd(8) or
    postlogd(8). 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 a sender or recipient address to have `-' as the first
    character.




Available with Postfix version 2.7 and later:



  

  
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





  

  
The minimal delay between warnings that a specific destination is clogging
      up the Postfix active queue.

  

  
The maximal number of messages in the active queue.

  

  
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.

  

  
The minimal number of in-memory recipients for any message.

  

  
The default per-transport upper limit on the number of in-memory
      recipients.

  

  
A transport-specific override for the default_recipient_limit parameter
      value, where transport is the master.cf name of the message
      delivery transport.

  

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

  

  
A transport-specific override for the default_extra_recipient_limit
      parameter value, where transport is the master.cf name of the
      message delivery transport.




Available in Postfix version 2.4 and later:



  

  
The default per-transport limit on the number of recipients refilled at
      once.

  

  
A transport-specific override for the default_recipient_refill_limit
      parameter value, where transport is the master.cf name of the
      message delivery transport.

  

  
The default per-transport maximum delay between refilling recipients.

  

  
A transport-specific override for the default_recipient_refill_delay
      parameter value, where transport is the master.cf name of the
      message delivery transport.








DELIVERY CONCURRENCY CONTROLS





  

  
The initial per-destination concurrency level for parallel delivery to the
      same destination.

  

  
The default maximal number of parallel deliveries to the same
    destination.

  

  
A transport-specific override for the
      default_destination_concurrency_limit parameter value, where
      transport is the master.cf name of the message delivery
    transport.




Available in Postfix version 2.5 and later:



  

  
A transport-specific override for the initial_destination_concurrency
      parameter value, where transport is the master.cf name of the
      message delivery transport.

  

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

  

  
A transport-specific override for the
      default_destination_concurrency_failed_cohort_limit parameter value, where
      transport is the master.cf name of the message delivery
    transport.

  

  
The per-destination amount of delivery concurrency negative feedback,
      after a delivery completes with a connection or handshake failure.

  

  
A transport-specific override for the
      default_destination_concurrency_negative_feedback parameter value, where
      transport is the master.cf name of the message delivery
    transport.

  

  
The per-destination amount of delivery concurrency positive feedback,
      after a delivery completes without connection or handshake failure.

  

  
A transport-specific override for the
      default_destination_concurrency_positive_feedback parameter value, where
      transport is the master.cf name of the message delivery
    transport.

  

  
Make the queue manager's feedback algorithm verbose for performance
      analysis purposes.








RECIPIENT SCHEDULING CONTROLS





  

  
The default maximal number of recipients per message delivery.

  

  
A transport-specific override for the default_destination_recipient_limit
      parameter value, where transport is the master.cf name of the
      message delivery transport.








MESSAGE SCHEDULING CONTROLS





  

  
How often the Postfix queue manager's scheduler is allowed to preempt
      delivery of one message with another.

  

  
A transport-specific override for the default_delivery_slot_cost parameter
      value, where transport is the master.cf name of the message
      delivery transport.

  

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

  

  
A transport-specific override for the default_minimum_delivery_slots
      parameter value, where transport is the master.cf name of the
      message delivery transport.

  

  
The default value for transport-specific _delivery_slot_discount
    settings.

  

  
A transport-specific override for the default_delivery_slot_discount
      parameter value, where transport is the master.cf name of the
      message delivery transport.

  

  
The default value for transport-specific _delivery_slot_loan
    settings.

  

  
A transport-specific override for the default_delivery_slot_loan parameter
      value, where transport is the master.cf name of the message
      delivery transport.








OTHER RESOURCE AND RATE CONTROLS





  

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

  

  
The maximal time between attempts to deliver a deferred message.

  

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

  

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

  

  
The time between attempts by the Postfix queue manager to contact a
      malfunctioning message delivery transport.




Available in Postfix version 2.1 and later:



  

  
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:



  

  
The default amount of delay that is inserted between individual message
      deliveries to the same destination and over the same message delivery
      transport.

  

  
A transport-specific override for the default_destination_rate_delay
      parameter value, where transport is the master.cf name of the
      message delivery transport.




Available in Postfix version 3.1 and later:



  

  
The default amount of delay that is inserted between individual message
      deliveries over the same message delivery transport, regardless of
      destination.

  

  
A transport-specific override for the default_transport_rate_delay
      parameter value, where the initial transport in the parameter name
      is the master.cf name of the message delivery transport.








SAFETY CONTROLS





  

  
How much time a Postfix queue manager process may take to handle a request
      before it is terminated by a built-in watchdog timer.

  

  
The time limit for the queue manager to send or receive information over
      an internal communication channel.




Available in Postfix version 3.1 and later:



  

  
A safety limit that prevents address verification requests from
      overwhelming the Postfix queue.








MISCELLANEOUS CONTROLS





  

  
The default location of the Postfix main.cf and master.cf configuration
      files.

  

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

  

  
The maximal number of digits after the decimal point when logging
      sub-second delay values.

  

  
Log warnings about problematic configuration settings, and provide helpful
      suggestions.

  

  
The process ID of a Postfix command or daemon process.

  

  
The process name of a Postfix command or daemon process.

  

  
The location of the Postfix top-level queue directory.

  

  
The syslog facility of Postfix logging.

  

  
A prefix that is prepended to the process name in syslog records, so that,
      for example, "smtpd" becomes "prefix/smtpd".




Available in Postfix version 3.0 and later:



  

  
After sending a "your message is delayed" notification, inform
      the sender when the delay clears up.




Available in Postfix 3.3 and later:



  

  
The master.cf service name of a Postfix daemon process.




Available in Postfix 3.5 and later:



  

  
The email address form that will be used in non-debug logging (info,
      warning, etc.).








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
postlogd(8), Postfix logging
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
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA