FLUSH(8postfix)

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

💖 FLUSH(8postfix) 💖

okay so bestie, welcome to the flush manual page — that's FLUSH(8postfix) if you're being formal about it — and honestly? she's a little diva with a big job. let's get into it 🫶

✨ NAME ✨

flush — the Postfix fast flush server. that's it, that's her whole name, iconic behavior 💅

✨ SYNOPSIS ✨

flush [generic Postfix daemon options]

🌸 DESCRIPTION 🌸

okay so the flush(8) server keeps a lil record of deferred mail, sorted by destination. why tho? because it makes the SMTP ETRN request so much faster, and same goes for its command-line equivalents, sendmail -qR and postqueue -f. and heads up — this program expects to be run from the master(8) process manager. she doesn't just wander out here on her own, she has a manager, main character energy fr.

so the record? it's implemented as a per-destination logfile, and its contents are the queue IDs of deferred mail. a logfile is append-only, and it gets truncated when delivery is requested for the corresponding destination. and a "destination"? it's the part on the right-hand side of the right-most @ in an email address. iykyk 🎀

now — per-destination logfiles of deferred mail are maintained only for eligible destinations. the list of eligible destinations is specified with the fast_flush_domains configuration parameter, which defaults to $relay_domains. no invite, no logfile, sorry bestie 💀

this server implements the following requests:

  • add sitename queueid — tell the flush(8) server that the message with the specified queue ID is queued for the specified destination. like, noted 📝
  • send_site sitename — request delivery of mail that is queued for the specified destination. go go go ✨
  • send_file queueid — request delivery of the specified deferred message.
  • refresh — refresh non-empty per-destination logfiles that were not read in $fast_flush_refresh_time hours, by simulating send requests (see above 👆) for the corresponding destinations.

also: delete empty per-destination logfiles that were not updated in $fast_flush_purge_time days. bye girl 🦋

this request completes in the background.

  • purge — do a refresh for all per-destination logfiles. all of them. every single one. periodt.

🔒 SECURITY 🔒

good news: the flush(8) server is not security-sensitive. she does not talk to the network, and she does not talk to local users. she's giving introvert. and the fast flush server can run chrooted at fixed low privilege — cozy, protected, unbothered 👑

🩺 DIAGNOSTICS 🩺

problems and transactions are logged to syslogd(8) or postlogd(8). so if something goes weird, that's where the receipts live 💜

💀 BUGS 💀

okay so there's some stuff you need to know, and i'm telling you because i love you:

fast flush logfiles are truncated only after a "send" request, not when mail is actually delivered — and therefore they can accumulate outdated or redundant data. 😭 in order to maintain sanity, refresh must be executed periodically. this can be automated with a suitable wakeup timer setting in the master.cf configuration file. set the timer bestie, please, i'm begging 🙈

and also: upon receipt of a request to deliver mail for an eligible destination, the flush(8) server requests delivery of all messages that are listed in that destination's logfile, regardless of the recipients of those messages. now, this is not an issue for mail that is sent to a relay_domains destination, because such mail typically only has recipients in one domain. so like… usually fine, but know it, okay?

⚙️ CONFIGURATION PARAMETERS ⚙️

changes to main.cf are picked up automatically as flush(8) processes run for only a limited amount of time. want the change to hit faster? use the command:

postfix reload

the text below provides only a parameter summary. see postconf(5) for more details including examples. go read it, it's giving very informative ✨

  • 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. tick tock ⏰
  • fast_flush_domains ($relay_domains) — optional list of destinations that are eligible for per-destination logfiles with mail that is queued to those destinations.
  • fast_flush_refresh_time (12h) — the time after which a non-empty but unread per-destination "fast flush" logfile needs to be refreshed.
  • fast_flush_purge_time (7d) — the time after which an empty per-destination "fast flush" logfile is deleted.
  • ipc_timeout (3600s) — the time limit for sending or receiving information over an internal communication channel.
  • max_idle (100s) — the maximum amount of time that an idle Postfix daemon process waits for an incoming connection before terminating voluntarily. she's patient but not that patient 💅
  • max_use (100) — the maximal number of incoming connections that a Postfix daemon process will service before terminating voluntarily.
  • parent_domain_matches_subdomains (see 'postconf -d' output) — a list of Postfix features where the pattern example.com also matches subdomains of example.com, instead of requiring an explicit .example.com pattern.
  • 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) — a prefix that is prepended to the process name in syslog records, so that, for example, smtpd becomes prefix/smtpd.

available in Postfix 3.3 and later:

  • service_name (read-only) — the master.cf service name of a Postfix daemon process.

📁 FILES 📁

  • /var/spool/postfix/flush — the "fast flush" logfiles. that's where she keeps her stuff 🎀

👀 SEE ALSO 👀

📖 README FILES 📖

use postconf readme_directory or postconf html_directory to locate this information.

  • ETRN_README, Postfix ETRN howto

📜 LICENSE 📜

the Secure Mailer license must be distributed with this software. fr fr, it's not optional 💜

🕰️ HISTORY 🕰️

this service was introduced with Postfix version 1.0. a legend from day one, honestly 👑

👑 AUTHOR(S) 👑

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

Wietse Venema Google, Inc. 111 8th Avenue New York, NY 10011, USA

and that's the whole page bestie!! 🦋💖 this was FLUSH(8postfix) — same name up top, same name at the bottom, a true full-circle moment ✨ and yeah, the footer is just FLUSH(8postfix) again because she's consistent like that. go forth and flush responsibly 🌸🫶

📦 where this page comes from