mbox(5) 			 User Manuals			       mbox(5)



NAME
       mbox - Format for mail message storage.

DESCRIPTION
       This  document describes the format traditionally used by Unix hosts to
       store mail messages locally.  mbox files typically reside in  the  sys
       tems  mail  spool, under various names in users Mail directories, and
       under the name mbox in users home directories.

       An mbox is a text file containing an arbitrary number  of  e-mail  mes
       sages.  Each message consists of a postmark, followed by an e-mail mes
       sage formatted according to RFC822, RFC2822. The file format  is  line-
       oriented. Lines are separated by line feed characters (ASCII 10).

       A  postmark  line consists of the four characters "From", followed by a
       space character, followed by the  messages  envelope  sender  address,
       followed  by  whitespace,  and  followed  by a time stamp. This line is
       often called From_ line.

       The sender address is expected to be addr-spec as  defined  in  RFC2822
       3.4.1.  The date is expected to be date-time as defined in RFC2822 3.3.
       For compatibility reasons with legacy software, two-digit years greater
       than  or  equal	to  70 should be interpreted as the years 1970+, while
       two-digit years less  than  70  should  be  interpreted	as  the  years
       2000-2069.  Software  reading  files in this format should also be pre
       pared to accept non-numeric timezone information such as "CET DST"  for
       Central European Time, daylight saving time.

       Example:

	>From example@example.com Fri Jun 23 02:56:55 2000

       In  order  to  avoid misinterpretation of lines in message bodies which
       begin with the four characters "From", followed by a  space  character,
       the  mail  delivery  agent  must quote any occurrence of "From " at the
       start of a body line.

       There are two different quoting schemes, the first (MBOXO) only	quotes
       plain  "From  "	lines in the body by prepending a > to the line; the
       second (MBOXRD) also quotes already quoted "From " lines by  prepending
       a > (i.e. ">From ", ">>From ", ...). The later has the advantage that
       lines like

	>From the command line you can use the -p option

       arent dequoted wrongly as a MBOXRD-MDA would turn the line into

	>>From the command line you can use the -p option

       before storing it. Besides MBOXO and MBOXRD there is also MBOXCL  which
       is MBOXO with a "Content-Length:"-field with the number of bytes in the
       message body; some MUAs (like mutt(1)) do automatically transform MBOXO
       mailboxes into MBOXCL ones when ever they write them back as MBOXCL can
       be read by any MBOXO-MUA without any problems.

       If the modification-time (usually determined via stat(2)) of a nonempty
       mbox  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.

LOCKING
       Since mbox files are frequently accessed by multiple programs in paral
       lel, mbox 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
	      mbox  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.

	     Dotlocking  is used on all kinds of systems. In order to lock an
	      mbox file named folder, an application first creates a temporary
	      file  with  a  unique  name in the directory in which the folder
	      resides. The application then tries to use  the  link(2)	system
	      call  to	create	a hard link named folder.lock to the temporary
	      file. The success of the link(2) system call should be addition
	      ally  verified  using  stat(2) calls. If the link has succeeded,
	      the mail folder is considered dotlocked. The temporary file  can
	      then safely be unlinked.

	      In  order  to  release the lock, an application just unlinks the
	      folder.lock file.

       If multiple methods are combined, implementors 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 mbox 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 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 mbox files. Failure to do so may  result  in
       loss of e-mail data, and in corrupted mbox files.

FILES
       /var/spool/mail/$LOGNAME
	      $LOGNAMEs incoming mail folder.

       $HOME/mbox
	      users archived mail messages, in his $HOME directory.

       $HOME/Mail/
	      A  directory in users $HOME directory which is commonly used to
	      hold mbox format folders.


SEE ALSO
       mutt(1), fcntl(2), flock(2),  link(2),  stat(2),  maildir(5),  mmdf(5),
       RFC822, RFC976, RFC2822

AUTHOR
       Thomas	  Roessler    ,	Urs    Janssen
       

HISTORY
       The mbox format occurred in Version 6 AT&T Unix.
       A variant of this format was documented in RFC976.



Unix			      February 19th, 2002		       mbox(5)