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<title>Filtering Mail with Sendmail</title>
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<h1>Filtering Mail with Sendmail</h1>
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<P><b>Disclaimer</b>:
This preliminary API description is provided for review only. This
specification may change based on feedback from reviewers, and does
not bind Sendmail to offer this functionality in any release.
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<h2>Introduction</h2>
<P>
Sendmail's Content Management API (milter) provides third-party
programs to access mail messages as they are being processed by the
Mail Transfer Agent (MTA), allowing them to examine and modify message
content and meta-information. Filtering policies implemented by
Milter-conformant filters may then be centrally configured and
composed in an end-user's MTA configuration file.
<p>
Possible uses for filters include spam rejection, virus
filtering, and content control. In general, Milter seeks to address
site-wide filtering concerns in a scalable way. Individual users' mail
filtering needs (e.g. sorting messages by subject) are left to
client-level programs such as <a href="http://www.procmail.org">Procmail</a>.
<P>
This document is a technical introduction intended for those
interested in developing Milter filters. It includes:
<ul>
<li>A description of Milter's design goals.
<li>An explanation of Milter application architecture, including
interactions between the support library and user code, and between
filters and the MTA.
<li>A specification of the C application programming interface.
<li>An example of a simple Milter filter.
</ul>
<h2>Contents</h2>
<ul>
<li><a href="design.html">Architecture</a>
<ul>
<li>Design Goals
<li>Implementing Filtering Policies
<li>MTA - Filter communication
</ul>
<li><a href="overview.html">Technical Overview</a>
<ul>
<li>Initialization
<li>Control flow
<li>Multithreading
<li>Resource Management
<li>Signal Handling
</ul>
<li><a href="api.html">API Documentation</a>
<ul>
<li>Library Control Functions
<li>Data Access Functions
<li>Message Modification Functions
<li>Callbacks
</ul>
<li><a href="installation.html">Installation and Configuration</a>
<ul>
<li>Compiling and Installing Your Filter
<li>Configuring Sendmail
</ul>
<li><a href="sample.html">A Sample Filter</a>
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Copyright (c) 2000, 2001, 2003 Sendmail, Inc. and its suppliers.
All rights reserved.
<br>
By using this file, you agree to the terms and conditions set
forth in the LICENSE.
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