Ubuntu Manpage: qmgr - Postfix queue manager

Provided by: postfix_2.11.0-1ubuntu1.2_amd64

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 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)
              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.

       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)
              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 depends on the value of the corresponding
              per-destination recipient 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 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

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(8postfix)