Section: User Manuals (5)
Updated: February 18th, 2002
An MMDF mailbox is a text file containing an arbitrary number of e-mail messages. Each message consists of a postmark, followed by an e-mail message formatted according to RFC822 / RFC2822, followed by a postmark. The file format is line-oriented. Lines are separated by line feed characters (ASCII 10). A postmark line consists of the four characters "^A^A^A^A" (Control-A; ASCII 1).
>From what I learned about the MMDF-format:
Subject: test 2
In contrast to most other single file mailbox formats like MBOXO and MBOXRD (see mbox?(5)) there is no need to quote/dequote "From "-lines in MMDF mailboxes as such lines have no special meaning in this format.
If the modification-time (usually determined via stat?(2)) of a nonempty mailbox file is greater than the access-time the file has new mail. Many MUAs place a Status: header in each message to indicate which messages have already been read.
Since MMDF files are frequently accessed by multiple programs in parallel, MMDF files should generally not be accessed without locking.
Three different locking mechanisms (and combinations thereof) are in general use:
If multiple methods are combined, an MMDF file must not be considered to have been successfully locked before all individual locks were obtained. When one of the individual locking methods fails, an application should release all locks it acquired successfully, and restart the entire locking procedure from the beginning, after a suitable delay.
The locking mechanism used on a particular system is a matter of local policy, and should be consistently used by all applications installed on the system which access MMDF files. Failure to do so may result in loss of e-mail data, and in corrupted MMDF files.
Urs Janssen <firstname.lastname@example.org>
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