+++ /dev/null
-.\" Project : tin
-.\" Module : mmdf.5
-.\" Author : U. Janssen
-.\" Created : 2002-02-18
-.\" Updated :
-.\" Notes : needs a lot of work
-.\"
-.TH mmdf 5 "February 18th, 2002" "Unix" "User Manuals"
-.\"
-.SH NAME
-MMDF \- Multi\-channel Memorandum Distribution Facility mailbox format
-.\"
-.SH DESCRIPTION
-This document describes the
-.B MMDF
-mailbox format used by some MTAs and MUAs (i.e.
-.BR scomail (1))
-to store mail messages locally.
-.PP
-An
-.B 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 \fBRFC822\fP / \fBRFC2822\fP, 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).
-.TP
-Example of a \fBMMDF\fP mailbox holding two mails:
-.RS
-.nf
-.sp
-^A^A^A^A
-.br
-From: example@example.com
-.br
-To: example@example.org
-.br
-Subject: test
-.br
-.sp
-.br
->From what I learned about the MMDF-format:
-.br
-.br
-^A^A^A^A
-.br
-^A^A^A^A
-.br
-From: example@example.com
-.br
-To: example@example.org
-.br
-Subject: test 2
-.br
-.sp
-.br
-bar
-.br
-^A^A^A^A
-.fi
-.RE
-.PP
-In contrast to most other single file mailbox formats like
-MBOXO and MBOXRD (see
-.BR mbox (5))
-there is no need to quote/dequote "From "\-lines in
-.B MMDF
-mailboxes as such lines have no special meaning in this format.
-.PP
-If the modification-time (usually determined via
-.BR 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.
-.\"
-.SH LOCKING
-Since
-.B MMDF
-files are frequently accessed by multiple programs in parallel,
-.B MMDF
-files should generally not be accessed without locking.
-.PP
-Three different locking mechanisms (and combinations thereof) are in
-general use:
-.IP "\(bu"
-.BR fcntl (2)
-locking is mostly used on recent, POSIX-compliant systems. Use of
-this locking method is, in particular, advisable if
-.B MMDF
-files are accessed through the Network File System (NFS), since it
-seems the only way to reliably invalidate NFS clients' caches.
-.IP "\(bu"
-.BR flock (2)
-locking is mostly used on BSD-based systems.
-.IP "\(bu"
-Dotlocking is used on all kinds of systems. In order to lock an
-.B MMDF
-file named \fIfolder\fR, an application first creates a temporary file
-with a unique name in the directory in which the
-\fIfolder\fR resides. The application then tries to use the
-.BR link (2)
-system call to create a hard link named \fIfolder.lock\fR
-to the temporary file. The success of the
-.BR link (2)
-system call should be additionally verified using
-.BR stat (2)
-calls. If the link has succeeded, the mail folder is considered
-dotlocked. The temporary file can then safely be unlinked.
-.IP ""
-In order to release the lock, an application just unlinks the
-\fIfolder.lock\fR file.
-.PP
-If multiple methods are combined, implementors should make sure to
-use the non-blocking variants of the
-.BR fcntl (2)
-and
-.BR flock (2)
-system calls in order to avoid deadlocks.
-.PP
-If multiple methods are combined, an
-.B 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.
-.PP
-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
-.B MMDF
-files. Failure to do so may result in loss of e-mail data, and in
-corrupted
-.B MMDF
-files.
-.\"
-.\" .SH FILES
-.\" /usr/spool/mmdf/lock/home
-.\" $HOME/Mail/
-.\"
-.\" .SH SECURITY
-.\"
-.SH "CONFORMING TO"
-.B MMDF
-is not part of any currently supported standard.
-.\"
-.SH HISTORY
-.B MMDF
-was developed at the University of Delaware by Dave Crocker.
-.\"
-.SH "SEE ALSO"
-.BR scomail (1),
-.BR fcntl (2),
-.BR flock (2),
-.BR link (2),
-.BR stat (2),
-.BR mbox (5),
-.BR RFC822 ,
-.BR RFC2822
-
-.SH AUTHOR
-Urs Janssen <urs@tin.org>
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