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mmdf(5) User Manuals mmdf(5) NAME MMDF - Multi-channel Memorandum Distribution Facility mailbox format DESCRIPTION This document describes the MMDF mailbox format used by some MTAs and MUAs (i.e. scomail(1)) to store mail messages locally. 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 post- mark. The file format is line-oriented. Lines are separated by line feed characters (ASCII 10). A postmark line consists of the four char- acters "^A^A^A^A" (Control-A; ASCII 1). Example of a MMDF mailbox holding two mails: ^A^A^A^A From: example@example.com To: example@example.org Subject: test >From what I learned about the MMDF-format: ^A^A^A^A ^A^A^A^A From: example@example.com To: example@example.org Subject: test 2 bar ^A^A^A^A 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 mes- sages have already been read. LOCKING Since MMDF files are frequently accessed by multiple programs in paral- lel, MMDF files should generally not be accessed without locking. Three different locking mechanisms (and combinations thereof) are in general use: • fcntl(2) locking is mostly used on recent, POSIX-compliant sys- tems. Use of this locking method is, in particular, advisable if MMDF files are accessed through the Network File System (NFS), since it seems the only way to reliably invalidate NFS clients' caches. • flock(2) locking is mostly used on BSD-based systems. If multiple methods are combined, implementers should make sure to use the non-blocking variants of the fcntl(2) and flock(2) system calls in order to avoid deadlocks. If multiple methods are combined, an MMDF file must not be considered to have been successfully locked before all individual locks were ob- tained. When one of the individual locking methods fails, an applica- tion 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. CONFORMING TO MMDF is not part of any currently supported standard. HISTORY MMDF was developed at the University of Delaware by Dave Crocker. SEE ALSO scomail(1), fcntl(2), flock(2), link(2), stat(2), mbox(5), RFC822, RFC2822 AUTHOR Urs Janssen <urs@tin.org> Unix 2002-02-18 mmdf(5)
NAME | DESCRIPTION | LOCKING | CONFORMING TO | HISTORY | SEE ALSO | AUTHOR
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