QMGR(8postfix)

📦 version 3.8.6, in debian bookworm, ubuntu jammy, ubuntu noble

👑 qmgr — the Postfix queue manager 💖

okay bestie, sit DOWN, because this is the girl who runs the whole mailroom — qmgr(8postfix). She's the queue manager. She doesn't do drama, she does deliveries. ✨

🌸 NAME

qmgr — Postfix queue manager 🎀

🦋 SYNOPSIS

qmgr [generic Postfix daemon options]

💅 DESCRIPTION

So the qmgr(8) daemon is literally just sitting there, waiting for incoming mail to show up, and then she arranges for it to get delivered through the Postfix delivery processes. That's her whole job and she does it flawlessly, no cap. 💖

The actual routing strategy? Not her problem, she delegates that to the trivial-rewrite(8) daemon. Iconic delegation behavior, honestly.

Heads up: this program expects to be run from the master(8) process manager. That's her whole support system. 🫶

Mail that's addressed to the local double-bounce address gets logged and then discarded. And why? Because it stops potential loops caused by undeliverable bounce notifications. It's giving "we don't do infinite loops in this house." 💀

🌈 MAIL QUEUES

The qmgr(8) daemon maintains the following queues, and each one has a whole personality:

  • incoming — Inbound mail from the network, or mail that got picked up by the local pickup(8) daemon from the maildrop directory. Fresh arrivals, basically. ✨
  • active — Messages that the queue manager has opened for delivery. Only a limited number of messages is allowed to enter the active queue (that's the leaky bucket strategy, for a fixed delivery rate). It's giving VIP section with a strict guest list. 👑
  • deferred — Mail that could not be delivered upon the first attempt. The queue manager implements exponential backoff by doubling the time between delivery attempts. She's not ghosting you, she's just pacing herself. 😭
  • corrupt — Unreadable or damaged queue files get moved here for inspection. Not a vibe, but at least they're contained. 🙈
  • hold — Messages that are kept "on hold" stay here until someone sets them free. Literally just sitting in timeout until you say so. 🎀

🍓 DELIVERY STATUS REPORTS

The qmgr(8) daemon keeps an eye on per-message delivery status reports in these directories. Each status report file has the same name as the corresponding message file — cute matching set energy, love that for them. 💜

  • 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.

And the qmgr(8) daemon is the one responsible for asking the bounce(8), defer(8) or trace(8) daemons to send delivery reports. She's the group chat admin, fr fr. 💅

✨ STRATEGIES

The queue manager implements a variety of strategies for either opening queue files (input) or for message delivery (output). She contains multitudes. 🌸

  • 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. Emotional stability under pressure. 🫶
  • 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. Nobody gets left on read. 💖
  • slow start — This strategy eliminates "thundering herd" problems by slowly adjusting the number of parallel deliveries to the same destination. Not me starting with one delivery and easing in, no big deal. 🦋
  • round robin — The queue manager sorts delivery requests by destination. Round-robin selection prevents one destination from dominating deliveries to other destinations. Main character energy is banned here. 👑
  • 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. She remembers who's not answering. 💀
  • 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. It's giving genius behavior, lowkey. ⭐

🔥 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. Clearing out the block list. 🧹
  • 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. So, 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. She's reading the whole group chat at once and summarizing it. Efficiency queen. 💅

💜 STANDARDS

🎀 SECURITY

The qmgr(8) daemon is not security sensitive. She reads single-character messages from untrusted local users, and thus may be susceptible to denial of service attacks. Yeah. 😭

The qmgr(8) daemon does not talk to the outside world, and it can be run at fixed low privilege in a chrooted environment. Introvert queen, thriving in her little enclosed world. 🦋

🌟 DIAGNOSTICS

Problems and transactions are logged to syslogd(8) or postlogd(8). Corrupted message files are saved to the corrupt queue for further inspection. (We love a paper trail.) 📝

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.

Translation: she's one girl doing everything and sometimes the disk is fully booked. It's not her fault, it's the burst. 😭

⚙️ 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.

Bestie. She does NOT re-read the group chat. You have to ping her. postfix reload. Periodt. 💅

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 ($default_recipient_limit) — A transport-specific override for the default_recipient_limit parameter value, where transport is the master.cf name of the message delivery transport.
  • default_extra_recipient_limit (1000) — The default value for the extra per-transport limit imposed on the number of in-memory recipients.
  • transport_extra_recipient_limit ($default_extra_recipient_limit) — 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:

  • default_recipient_refill_limit (100) — The default per-transport limit on the number of recipients refilled at once.
  • transport_recipient_refill_limit ($default_recipient_refill_limit) — A transport-specific override for the default_recipient_refill_limit parameter value, where transport is the master.cf name of the message delivery transport.
  • default_recipient_refill_delay (5s) — The default per-transport maximum delay between recipients refills.
  • transport_recipient_refill_delay ($default_recipient_refill_delay) — 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 💖

okay so like, these are the knobs that control how many parallel deliveries go down to the same destination. it's giving traffic control but for emails. 🚦

  • initial_destination_concurrency (5) — the initial per-destination concurrency level for parallel delivery to the same destination. like how many besties you send in first. 💅
  • default_destination_concurrency_limit (20) — the default maximal number of parallel deliveries to the same destination. don't overwhelm them, okay? 🙈
  • transport_destination_concurrency_limit ($default_destination_concurrency_limit) — a transport-specific override for the default_destination_concurrency_limit parameter value, where transport is the master.cf name of the message delivery transport. so you can customize per transport. slay. ✨

🌟 Available in Postfix version 2.5 and later:

  • transport_initial_destination_concurrency ($initial_destination_concurrency) — a transport-specific override for the initial_destination_concurrency parameter value, where transport is the master.cf name of the message delivery transport. 🎀
  • default_destination_concurrency_failed_cohort_limit (1) — how many pseudo-cohorts must suffer connection or handshake failure before a specific destination is considered unavailable (and further delivery is suspended). so like, after this many fails, we ghost them. 💀
  • transport_destination_concurrency_failed_cohort_limit ($default_destination_concurrency_failed_cohort_limit) — 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. 🦋
  • 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. it's giving consequences. 😭
  • transport_destination_concurrency_negative_feedback ($default_destination_concurrency_negative_feedback) — a transport-specific override for the default_destination_concurrency_negative_feedback parameter value, where transport is the master.cf name of the message delivery transport. 💜
  • default_destination_concurrency_positive_feedback (1) — the per-destination amount of delivery concurrency positive feedback, after a delivery completes without connection or handshake failure. yay, good job! 🌈
  • transport_destination_concurrency_positive_feedback ($default_destination_concurrency_positive_feedback) — 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. ⭐
  • destination_concurrency_feedback_debug (no) — make the queue manager's feedback algorithm verbose for performance analysis purposes. so you can see all the drama. 👑

🎀 RECIPIENT SCHEDULING CONTROLS 🎀

  • default_destination_recipient_limit (50) — the default maximal number of recipients per message delivery. don't put too many people in the group chat. 💖
  • transport_destination_recipient_limit ($default_destination_recipient_limit) — 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 ✨

  • default_delivery_slot_cost (5) — how often the Postfix queue manager's scheduler is allowed to preempt delivery of one message with another. it's giving priority. 🔥
  • transport_delivery_slot_cost ($default_delivery_slot_cost) — a transport-specific override for the default_delivery_slot_cost parameter value, where transport is the master.cf name of the message delivery transport. 🦋
  • default_minimum_delivery_slots (3) — how many recipients a message must have in order to invoke the Postfix queue manager's scheduling algorithm at all. so if it's too small, it doesn't even get scheduled. 🙈
  • transport_minimum_delivery_slots ($default_minimum_delivery_slots) — a transport-specific override for the default_minimum_delivery_slots parameter value, where transport is the master.cf name of the message delivery transport. 💜
  • default_delivery_slot_discount (50) — the default value for transport-specific _delivery_slot_discount settings. lowkey a discount on slots. 💅
  • transport_delivery_slot_discount ($default_delivery_slot_discount) — a transport-specific override for the default_delivery_slot_discount parameter value, where transport is the master.cf name of the message delivery transport. 🎀
  • default_delivery_slot_loan (3) — the default value for transport-specific _delivery_slot_loan settings. loaning slots, like borrowing from a friend. 😭
  • transport_delivery_slot_loan ($default_delivery_slot_loan) — 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 🌟

  • minimal_backoff_time (300s) — the minimal time between attempts to deliver a deferred message; prior to Postfix 2.4 the default value was 1000s. so like, wait a bit before trying again. ⏳
  • maximal_backoff_time (4000s) — the maximal time between attempts to deliver a deferred message. don't wait forever. ⌛
  • 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. so after 5 days, it's a ghost. 👻
  • queue_run_delay (300s) — the time between deferred queue scans by the queue manager; prior to Postfix 2.4 the default value was 1000s. like checking your notifications. 📱
  • transport_retry_time (60s) — the time between attempts by the Postfix queue manager to contact a malfunctioning message delivery transport. give it a minute. ⏱️

🌈 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. bounces have feelings too. 💔

💫 Available in Postfix version 2.5 and later:

  • default_destination_rate_delay (0s) — the default amount of delay that is inserted between individual message deliveries to the same destination and over the same message delivery transport. slow down, bestie. 🐢
  • transport_destination_rate_delay ($default_destination_rate_delay) — 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:

  • default_transport_rate_delay (0s) — the default amount of delay that is inserted between individual message deliveries over the same message delivery transport, regardless of destination. no matter where it's going, chill. 🧘
  • transport_transport_rate_delay ($default_transport_rate_delay) — 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. yes, it's a double transport situation. 💅

🛡️ 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. don't take too long or the watchdog will get you. 🐕
  • qmgr_ipc_timeout (60s) — the time limit for the queue manager to send or receive information over an internal communication channel. like a texting timeout. 📵

🔒 Available in Postfix version 3.1 and later:

  • address_verify_pending_request_limit (see postconf -d output) — a safety limit that prevents address verification requests from overwhelming the Postfix queue. protect the queue at all costs. 🛡️

🧚 MISCELLANEOUS CONTROLS 🧚

  • config_directory (see postconf -d output) — the default location of the Postfix main.cf and master.cf configuration files. where the magic happens. 📁
  • defer_transports (empty) — the names of message delivery transports that should not deliver mail unless someone issues "sendmail -q" or equivalent. so they're on pause. ⏸️
  • delay_logging_resolution_limit (2) — the maximal number of digits after the decimal point when logging sub-second delay values. precision, bestie. 🔢
  • helpful_warnings (yes) — log warnings about problematic configuration settings, and provide helpful suggestions. because we care. 🫶
  • process_id (read-only) — the process ID of a Postfix command or daemon process. like a fingerprint. 🆔
  • process_name (read-only) — the process name of a Postfix command or daemon process. what's your name, bestie? 📛
  • queue_directory (see postconf -d output) — the location of the Postfix top-level queue directory. the main character's home. 🏠
  • syslog_facility (mail) — the syslog facility of Postfix logging. logging vibes. 📝
  • syslog_name (see postconf -d output) — a prefix that is prepended to the process name in syslog records, so that, for example, "smtpd" becomes "prefix/smtpd". it's giving personalization. 💅

🎉 Available in Postfix version 3.0 and later:

  • confirm_delay_cleared (no) — after sending a "your message is delayed" notification, inform the sender when the delay clears up. closure is important. 💌

💖 Available in Postfix 3.3 and later:

  • service_name (read-only) — the master.cf service name of a Postfix daemon process. what's their service? 🛎️

🌸 Available in Postfix 3.5 and later:

  • info_log_address_format (external) — the email address form that will be used in non-debug logging (info, warning, etc.). how you want to be addressed. 📧

📂 FILES 📂

  • /var/spool/postfix/incoming — incoming queue. the waiting room. 🚪
  • /var/spool/postfix/active — active queue. where the action is. ⚡
  • /var/spool/postfix/deferred — deferred queue. the time-out corner. ⏳
  • /var/spool/postfix/bounce — non-delivery status. boomerang. 🪃
  • /var/spool/postfix/defer — non-delivery status. more boomerang. 🪃
  • /var/spool/postfix/trace — delivery status. the receipts. 🧾

👀 SEE ALSO 👀

📖 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. so like, keep the license with it. 💼

👑 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

and that's the tea, bestie! this page is QMGR(8postfix) — that's the source/version — and the date is the date at the bottom of the manpage. iykyk. periodt. 💅✨

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