118 lines
3.7 KiB
HTML
118 lines
3.7 KiB
HTML
<html>
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<head>
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<title>Postfix Anatomy - Receiving Mail</title>
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</head>
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<body>
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<h1><a href="big-picture.html"><img src="small-picture.gif" width="115" height="45"></a> Postfix
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Anatomy - Receiving Mail</h1>
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<hr>
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<a href="index.html">Up one level</a> | Receiving Mail | <a
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href="delivering.html">Delivering Mail</a> | <a
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href="backstage.html">Behind the Scenes</a> | <a
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href="commands.html">Command-line Utilities</a>
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<p>
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When a message enters the Postfix mail system, the first stop on
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the inside is the <b>incoming</b> queue. The figure below shows
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the main components that are involved with new mail. For an
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explanation of the symbols used, click on the icon in the upper
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left-hand corner of this page.
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<p>
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<center>
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<img src="inbound.gif" width="497" height="213">
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</center>
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<p>
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<ul>
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<li>Mail is posted locally. The Postfix <a
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href="sendmail.1.html">sendmail</a> program deposits the message
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into the world-writable <b>maildrop</b> directory, where the message
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is picked up by the <a href="pickup.8.html">pickup</a> daemon.
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This daemon does some sanity checks, in order to protect the rest
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of the Postfix system. In order to avoid accidents, the directory
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permissions on the <b>maildrop</b> directory must be such that a
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user cannot delete someone elses mail.
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<p>
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<li>Mail comes in via the network. The Postfix <a href="smtpd.8.html">SMTP
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server</a> receives the message and does some sanity checks, in
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order to protect the rest of the Postfix system. The SMTP server
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can be configured to implement <a href="uce.html">UCE</a> controls
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on the basis of local or network-based black lists, DNS lookups,
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and other client request information.
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<p>
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<li>Mail is generated internally by the Postfix system itself, in
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order to return undeliverable mail to the sender. The <a
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href="bounce.8.html">bounce or defer</a> daemon brings the bad
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news.
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<p>
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<li>Mail is forwarded by the <a href="local.8.html">local</a>
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delivery agent, either via an entry in the system-wide <a
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href="aliases.5.html">alias</a> database, or via an entry in a
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per-user <a href="aliases.5.html">.forward</a> file. This is
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indicated with the unlabeled arrow.
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<p>
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<li>Mail is generated internally by the Postfix system itself, in
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order to notify the postmaster of a problem (this path is also
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indicated with the unlabeled arrow). The Postfix system can be
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configured to <a href="basic.html#notify">notify</a> the postmaster
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of SMTP protocol problems, UCE policy violations, and so on.
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<p>
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<li>The <a href="cleanup.8.html">cleanup</a> daemon implements the
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final processing stage for new mail. It adds missing <b>From:</b>
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and other message headers, arranges for address rewriting to the
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standard <i>user@fully.qualified.domain</i> form, and optionally
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extracts recipient addresses from message headers. The <b> cleanup</b>
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daemon inserts the result as a single queue file into the
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<b>incoming</b> queue, and notifies the <a href="qmgr.8.html">queue
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manager</a> of the arrival of new mail. The <b>cleanup</b> daemon
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can be configured to transform addresses on the basis of <a
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href="rewrite.html#canonical">canonical</a> and <a
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href="rewrite.html#virtual">virtual</a> table lookups.
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<p>
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<li>On request by the <b>cleanup</b> daemon, the <a
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href="trivial-rewrite.8.html">trivial-rewrite</a> daemon rewrites
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addresses to the standard <i>user@fully.qualified.domain</i> form.
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The initial Postfix version does not implement a rewriting language.
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Implementing one would take a lot of effort, and most sites do not
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need it. Instead, Postfix makes extensive use of <a
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href="rewrite.html">table lookup</a>.
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</ul>
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<hr>
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<a href="index.html">Up one level</a> | Receiving Mail | <a
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href="delivering.html">Delivering Mail</a> | <a
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href="backstage.html">Behind the Scenes</a> | <a
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href="commands.html">Command-line Utilities</a>
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</body>
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</html>
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