Postfix Overview - Introduction - SCN Research
Postfix Overview - Introduction - SCN Research
Postfix Overview - Introduction - SCN Research
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<strong>Postfix</strong> Anatomy - Behind the Scenes<br />
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<strong>Postfix</strong> Anatomy - Behind the Scenes<br />
Up one level | Receiving Mail | Delivering Mail | Behind the Scenes | Command-line Utilities<br />
The previous sections gave a simplified overview of how the <strong>Postfix</strong> system sends and receives mail. Several<br />
other things happen behind the scenes. Unfortunately, this is hard to visualize on a two-dimensional display, so<br />
this document has no illustration.<br />
• The master daemon is the supervisor process that keeps an eye on the well-being of the mail system. It is<br />
typically started at system boot time by the postfix command, and keeps running until the system goes<br />
down. The master daemon is responsible for starting all other <strong>Postfix</strong> daemon processes on demand, and<br />
for restarting daemons that terminated prematurely because of some problem. The master daemon is also<br />
responsible for enforcing the daemon process count limits as specified in the master.cf configuration file.<br />
• The bounce or defer daemon is called upon left and right by other daemon processes, in order to maintain<br />
per-message log files with non-delivery status information.<br />
• The trivial-rewrite daemon is called upon left and right by other daemon processes, in order to rewrite an<br />
address to user@fully.qualified.domain form, or in order to resolve a destination.<br />
• The showq daemon lists the <strong>Postfix</strong> queue status. This is the program behind the mailq command.<br />
• The flush daemon improves the performance of the SMTP ETRN request, and of its command-line<br />
equivalent, sendmail -qRdestination, for selected destinations. For other destinations, <strong>Postfix</strong> silently<br />
falls back to the equivalent of sendmail -q.<br />
• The spawn daemon listens on a TCP port, UNIX-domain socket or FIFO, and runs non-<strong>Postfix</strong><br />
commands on request, with the socket or FIFO connected to the standard input, output and error streams.<br />
It is currently used only in an example of the <strong>Postfix</strong> external content filtering system.<br />
Up one level | Receiving Mail | Delivering Mail | Behind the Scenes | Command-line Utilities<br />
http://www.porcupine.org/postfix-mirror/backstage.html<br />
6/26/01
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