查看“Postfix 基本设置指南”的源代码

=== Postfix的结构 ===

==== 组件 ====

下图表示Postfix系统的主要组件以及他们间的主要信息。

https://help.ubuntu.com/community/PostfixBasicSetupHowto?action=AttachFile&do=get&target=PostfixComponentsNw.gif

* 黄色椭圆表示邮件程序。
* 黄色方框表示邮件队列或文件。
* 蓝色方框表示查找的表。
* 大方框中的程序在Postfix主模块的控制下运行。
* 大方框中的数据记录Postfix系统的属性。

==== 接收邮件 ====

当一个新的消息进入Postfix系统，內部的第一站是在新进入队列（incoming queue）。下图表示了包含一个新邮件的主要组件。

[[File:attachment:PosfixRecieving.gif]]

* 邮件在本地发送。 Postfix的[http://www.postfix.org/sendmail.1.html sendmail]程序调用拥有特权的[http://www.postfix.org/postdrop.1.html postdrop]程序 which deposits the message into the '''maildrop''' directory, where the message is picked up by the [http://www.postfix.org/pickup.8.html pickup] daemon. This daemon does some sanity checks, in order to protect the rest of the Postfix system.
该程序将消息存放到 '''maildrop''' 目录，在那里消息被 [http://www.postfix.org/pickup.8.html pickup] 守护进程取走。pickup 守护进程为了保护其他的 Postfix 系统会执行一些完整性检测。
* Mail comes in via the network. The Postfix [http://www.postfix.org/smtpd.8.html SMTP server] receives the message and does some sanity checks, in order to protect the rest of the Postfix system. 
* 邮件从网络到来. Postfix 的[http://www.postfix.org/smtpd.8.html SMTP server]收到消息然后为了保护其他的 Postfix 系统作些完整性检测。 

* Mail is generated internally by the Postfix system itself, in order to return undeliverable mail to the sender. The [http://www.postfix.org/bounce.8.html bounce or defer] daemon brings the bad news.
*
* Mail is forwarded by the [http://www.postfix.org/local.8.html local] delivery agent, either via an entry in the system-wide [http://www.postfix.org/aliases.5.html alias] database, or via an entry in a per-user [http://www.postfix.org/aliases.5.html .forward] file. This is indicated with the unlabeled arrow.

* Mail is generated internally by the Postfix system itself, in order to [http://www.postfix.org/basic.html#notify notify] the postmaster of a problem (this path is also indicated with the unlabeled arrow).The Postfix system can be configured to notify the postmaster of SMTP protocol problems, [http://en.wikipedia.org/wiki/E-mail_spam UCE] policy violations, and so on.

* The [http://www.postfix.org/cleanup.8.html cleanup] daemon implements the final processing stage for new mail. It adds missing '''From:''' and other message headers, arranges for address rewriting to the standard user@fully.qualified.domain form, and optionally extracts recipient addresses from message headers. The '''cleanup''' daemon inserts the result as a single queue file into the '''incoming''' queue, and notifies the [http://www.postfix.org/qmgr.8.html queue manager] of the arrival of new mail. The '''cleanup''' daemon can be configured to transform addresses on the basis of [http://www.postfix.org/rewrite.html#canonical canonical] and [http://www.postfix.org/rewrite.html#virtual virtua] table lookups.

* On request by the cleanup daemon, the [http://www.postfix.org/trivial-rewrite.8.html trivial-rewrite] daemon rewrites addresses to the standard user@fully.qualified.domain form.