Postfix before-queue Milter support
Introduction
Postfix version 2.3 introduces support for the Sendmail version
8 Milter (mail filter) protocol. This protocol is used by applications
that run outside the MTA to inspect SMTP events (CONNECT, DISCONNECT),
SMTP commands (HELO, MAIL FROM, etc.) as well as mail content. All
this happens before mail is queued.
The reason for adding Milter support to Postfix is that there
exists a large collection of applications, not only to block unwanted
mail, but also to verify authenticity (examples: SenderID+SPF and
Domain keys)
or to digitally sign mail (example: Domain keys).
Having yet another Postfix-specific version of all that software
is a poor use of human and system resources.
Postfix 2.3 implements all the requests of Sendmail version 8
Milter protocols up to version 4, except one: message body replacement.
See, however, the
workarounds and limitations sections at the end of this
document.
This document provides information on the following topics:
