As of version 2.1, the Postfix SMTP server can forward all
incoming mail to a content filtering proxy server that inspects
all mail BEFORE it is stored in the Postfix mail queue.
The before-queue content filter is meant to be used as follows:
The before-queue content filter is not to be confused with the
approach described in the
FILTER_README document, where mail is
filtered AFTER it is stored in the Postfix mail queue.
This document describes the following topics: