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Postfix Documentation
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Postfix After-Queue Content Filter


This document requires Postfix version 2.1 or later.

Normally, Postfix receives mail, stores it in the mail queue and then delivers it. With the external content filter described here, mail is filtered AFTER it is queued. This approach decouples mail receiving processes from mail filtering processes, and gives you maximal control over how many filtering processes you are willing to run in parallel.

The after-queue content filter is meant to be used as follows:

Network or
local users
-> Postfix
-> Content
-> Postfix
-> Network or
local mailbox

This document describes implementations that use a single Postfix instance for everything: receiving, filtering and delivering mail. Applications that use two separate Postfix instances will be covered by a later version of this document.

The after-queue content filter is not to be confused with the approach that is described in the SMTPD_PROXY_README document, where incoming SMTP mail is filtered BEFORE it is stored into the Postfix queue.

This document describes two approaches to content filter all email, as well as several options to filter mail selectively:

Postfix Documentation
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