.TH OQMGR 8 
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.SH NAME
oqmgr
\-
old Postfix queue manager
.SH SYNOPSIS
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\fBoqmgr\fR [generic Postfix daemon options]
.SH DESCRIPTION
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The \fBoqmgr\fR 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
\fBtrivial-rewrite\fR(8) daemon.
This program expects to be run from the \fBmaster\fR(8) process
manager.

Mail addressed to the local \fBdouble-bounce\fR address is
logged and discarded.  This stops potential loops caused by
undeliverable bounce notifications.
.SH MAIL QUEUES
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The \fBoqmgr\fR daemon maintains the following queues:
.IP \fBincoming\fR
Inbound mail from the network, or mail picked up by the
local \fBpickup\fR agent from the \fBmaildrop\fR directory.
.IP \fBactive\fR
Messages that the queue manager has opened for delivery. Only
a limited number of messages is allowed to enter the \fBactive\fR
queue (leaky bucket strategy, for a fixed delivery rate).
.IP \fBdeferred\fR
Mail that could not be delivered upon the first attempt. The queue
manager implements exponential backoff by doubling the time between
delivery attempts.
.IP \fBcorrupt\fR
Unreadable or damaged queue files are moved here for inspection.
.IP \fBhold\fR
Messages that are kept "on hold" are kept here until someone
sets them free.
.SH DELIVERY STATUS REPORTS
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The \fBoqmgr\fR 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:
.IP \fBbounce\fR
Per-recipient status information about why mail is bounced.
These files are maintained by the \fBbounce\fR(8) daemon.
.IP \fBdefer\fR
Per-recipient status information about why mail is delayed.
These files are maintained by the \fBdefer\fR(8) daemon.
.PP
The \fBoqmgr\fR daemon is responsible for asking the
\fBbounce\fR(8) or \fBdefer\fR(8) daemons to send non-delivery
reports.
.SH STRATEGIES
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The queue manager implements a variety of strategies for
either opening queue files (input) or for message delivery (output).
.IP "\fBleaky bucket\fR"
This strategy limits the number of messages in the \fBactive\fR queue
and prevents the queue manager from running out of memory under
heavy load.
.IP \fBfairness\fR
When the \fBactive\fR queue has room, the queue manager takes one
message from the \fBincoming\fR queue and one from the \fBdeferred\fR
queue. This prevents a large mail backlog from blocking the delivery
of new mail.
.IP "\fBslow start\fR"
This strategy eliminates "thundering herd" problems by slowly
adjusting the number of parallel deliveries to the same destination.
.IP "\fBround robin\fR
The queue manager sorts delivery requests by destination.
Round-robin selection prevents one destination from dominating
deliveries to other destinations.
.IP "\fBexponential backoff\fR"
Mail that cannot be delivered upon the first attempt is deferred.
The time interval between delivery attempts is doubled after each
attempt.
.IP "\fBdestination status cache\fR"
The queue manager avoids unnecessary delivery attempts by
maintaining a short-term, in-memory list of unreachable destinations.
.SH TRIGGERS
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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):
.IP "\fBD (QMGR_REQ_SCAN_DEFERRED)\fR"
Start a deferred queue scan.  If a deferred queue scan is already
in progress, that scan will be restarted as soon as it finishes.
.IP "\fBI (QMGR_REQ_SCAN_INCOMING)\fR"
Start an incoming queue scan. If an incoming queue scan is already
in progress, that scan will be restarted as soon as it finishes.
.IP "\fBA (QMGR_REQ_SCAN_ALL)\fR"
Ignore deferred queue file time stamps. The request affects
the next deferred queue scan.
.IP "\fBF (QMGR_REQ_FLUSH_DEAD)\fR"
Purge all information about dead transports and destinations.
.IP "\fBW (TRIGGER_REQ_WAKEUP)\fR"
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.
.PP
The \fBoqmgr\fR daemon reads an entire buffer worth of triggers.
Multiple identical trigger requests are collapsed into one, and
trigger requests are sorted so that \fBA\fR and \fBF\fR precede
\fBD\fR and \fBI\fR. Thus, in order to force a deferred queue run,
one would request \fBA F D\fR; in order to notify the queue manager
of the arrival of new mail one would request \fBI\fR.
.SH STANDARDS
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None. The \fBoqmgr\fR daemon does not interact with the outside world.
.SH SECURITY
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The \fBoqmgr\fR 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 \fBoqmgr\fR daemon
does not talk to the outside world, and it can be run at fixed low
privilege in a chrooted environment.
.SH DIAGNOSTICS
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Problems and transactions are logged to the syslog daemon.
Corrupted message files are saved to the \fBcorrupt\fR queue
for further inspection.

Depending on the setting of the \fBnotify_classes\fR parameter,
the postmaster is notified of bounces and of other trouble.
.SH BUGS
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A single queue manager process has to compete for disk access with
multiple front-end processes such as \fBsmtpd\fR. A sudden burst of
inbound mail can negatively impact outbound delivery rates.
.SH CONFIGURATION PARAMETERS
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The following \fBmain.cf\fR parameters are especially relevant to
this program. See the Postfix \fBmain.cf\fR file for syntax details
and for default values. Use the \fBpostfix reload\fR command after
a configuration change.
.SH Miscellaneous
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.IP \fBallow_min_user\fR
Do not bounce recipient addresses that begin with '-'.
.IP \fBqueue_directory\fR
Top-level directory of the Postfix queue.
.SH "Active queue controls"
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.IP \fBqmgr_clog_warn_time\fR
Minimal delay between warnings that a specific destination
is clogging up the active queue. Specify 0 to disable.
.IP \fBqmgr_message_active_limit\fR
Limit the number of messages in the active queue.
.IP \fBqmgr_message_recipient_limit\fR
Limit the number of in-memory recipients.
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This parameter also limits the size of the short-term, in-memory
destination cache.
.SH "Timing controls"
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.IP \fBminimal_backoff_time\fR
Minimal time in seconds between delivery attempts
of a deferred message.
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This parameter also limits the time an unreachable destination
is kept in the short-term, in-memory destination status cache.
.IP \fBmaximal_backoff_time\fR
Maximal time in seconds between delivery attempts
of a deferred message.
.IP \fBmaximal_queue_lifetime\fR
Maximal time (default: in days) a regular message is queued
before it is considered undeliverable.
.IP \fBbounce_queue_lifetime\fR
Maximal time (default: in days) a bounce message is queued
before it is considered undeliverable.
.IP \fBqueue_run_delay\fR
Time in seconds between deferred queue scans. Queue scans do
not overlap.
.IP \fBtransport_retry_time\fR
Time in seconds between attempts to contact a broken
delivery transport.
.SH "Concurrency controls"
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In the text below, \fItransport\fR is the first field in a
\fBmaster.cf\fR entry.
.IP "\fBqmgr_fudge_factor\fR (valid range: 10..100)"
The percentage of delivery resources that a busy mail system will
use up for delivery of a large mailing list message.
With 100%, delivery of one message does not begin before the previous
message has been delivered. This results in good performance for large
mailing lists, but results in poor response time for one-to-one mail.
With less than 100%, response time for one-to-one mail improves,
but large mailing list delivery performance suffers. In the worst
case, recipients near the beginning of a large list receive a burst
of messages immediately, while recipients near the end of that list
receive that same burst of messages a whole day later.
.IP \fBinitial_destination_concurrency\fR
Initial per-destination concurrency level for parallel delivery
to the same destination.
.IP \fBdefault_destination_concurrency_limit\fR
Default limit on the number of parallel deliveries to the same
destination.
.IP \fItransport\fB_destination_concurrency_limit\fR
Limit on the number of parallel deliveries to the same destination,
for delivery via the named message \fItransport\fR.
.SH "Recipient controls"
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.IP \fBdefault_destination_recipient_limit\fR
Default limit on the number of recipients per message transfer.
.IP \fItransport\fB_destination_recipient_limit\fR
Limit on the number of recipients per message transfer, for the
named message \fItransport\fR.
.SH SEE ALSO
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master(8), process manager
syslogd(8) system logging
trivial-rewrite(8), address routing
.SH LICENSE
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The Secure Mailer license must be distributed with this software.
.SH AUTHOR(S)
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Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA