oqmgr - old Postfix queue manager

oqmgr [generic Postfix daemon options]

The oqmgr(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.

The oqmgr(8) daemon maintains the following queues:

incoming

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

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

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 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.

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 oqmgr(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.

None. The oqmgr(8) daemon does not interact with the outside world.

The oqmgr(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 oqmgr(8) daemon does not talk to the outside world, and it can be run at fixed low privilege in a chrooted environment.

Problems and transactions are logged to the syslog(8) 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.

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.

Changes to main.cf are not picked up automatically, as oqmgr(8) is a persistent process. Use the command "postfix reload" 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.

allow_min_user (no)

Allow a recipient address to have `-' as the first character.

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_fudge_factor (100)

Obsolete feature: the percentage of delivery resources that a busy mail system will use up for delivery of a large mailing list message.

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

Idem, for delivery via the named message transport.

default_destination_recipient_limit (50)

The default maximal number of recipients per message delivery.

transport_destination_recipient_limit

Idem, for delivery via the named message transport.

minimal_backoff_time (1000s)

The minimal time between attempts to deliver a deferred message.

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 (1000s)

The time between deferred queue scans by the queue manager.

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.

config_directory (see 'postconf -d' output)

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

daemon_timeout (18000s)

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

defer_transports (empty)

The names of message delivery transports that should not be delivered to unless someone issues "sendmail -q" or equivalent.

helpful_warnings (yes)

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

ipc_timeout (3600s)

The time limit for sending or receiving information over an internal communication channel.

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 (postfix)

The mail system name that is prepended to the process name in syslog records, so that "smtpd" becomes, for example, "postfix/smtpd".

/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

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

Use "postconf readme_directory" or "postconf html_directory" to locate this information.

QSHAPE_README, Postfix queue analysis

The Secure Mailer license must be distributed with this software.

Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA