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Postfix: The Definitive Guide by Kyle D. Dent

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Message Store Formats

When Postfix makes local deliveries it transfers the contents of messages to the local message store. The most common types of message stores are the traditional mbox format and the newer maildir style. Both use regular files to store messages, but they are structured in different ways. In Postfix, you specify maildir style by including a trailing slash when you configure any mail file or directory parameters (see configuration information later in this chapter).

The Mbox Format

Historically, Unix systems have used a single file to store each user's email messages. This type of message store format is commonly referred to as mbox. Each message within the file starts with a line that begins with the word From. It is important that the string start on the first character of the line, and that there is a space after the end of the word. The From line is commonly referred to as From_ with an underscore character to indicate the space following the word. Don't confuse the From_ line used for separating messages within an mbox file with the From: line included in email message headers. The last line of a message is always a blank line.

A complete From_ line looks like the following:

From jmbrown@example.com Sun Feb  3 16:54:01 2002

As described, the line starts with the word From followed by a space. Following the space is an email address that is usually the envelope address of the message. Following the envelope address is the date of delivery in the common Unix date ...

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