phpman > man > mbox(5)

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 system's 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 messages.  Each message con‐
       sists of a postmark, followed by an e-mail message 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, fol‐
       lowed by the message's 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 ex‐
       pected to be date-time as output by asctime(3).  For compatibility reasons with legacy  soft‐
       ware,  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 prepared to accept non-numeric timezone informa‐
       tion such as "CET DST" for Central European Time, daylight saving time.

       Example:

        >From example AT 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 oc‐
       currence 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  advan‐
       tage that lines like

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

       aren't 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 "Con‐
       tent-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 parallel, 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 systems. Use of this lock‐
              ing 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 direc‐
              tory 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 additionally 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 vari‐
       ants 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 success‐
       fully 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 mbox files. Fail‐
       ure to do so may result in loss of e-mail data, and in corrupted mbox files.

FILES
       /var/spool/mail/$LOGNAME
              $LOGNAME's incoming mail folder.

       $HOME/mbox
              user's archived mail messages, in his $HOME directory.

       $HOME/Mail/
              A directory in user's $HOME directory which is commonly used to hold mbox format fold‐
              ers.

SEE ALSO
       mutt(1),  fcntl(2),  flock(2),  link(2),  stat(2),  asctime(3),  maildir(5), mmdf(5), RFC822,
       RFC976, RFC2822

AUTHOR
       Thomas Roessler <roessler AT does-not-exist.org>, Urs Janssen <urs AT tin.org>

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)