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  consists  of  a  postmark,
       followed  by  an e-mail message formatted according to RFC
       822.  The file format is line-oriented.  Lines  are  sepa-
       rated by line feed characters (ASCII 10).

       A  postmark  line  consists of the four characters "From",
       followed by a space character, followed by  the  message's
       envelope  sender address, followed by whitespace, and fol-
       lowed by a time stamp. The sender address is  expected  to
       be an addrspec as defined in appendix D of RFC 822.

       The date is expected to be formatted according to the fol-
       lowing syntax (represented in  the  augmented  Backus-Naur
       formalism used by RFC 822):

       mbox-date    =   weekday month day time [ timezone ] year
       weekday      =   "Mon" / "Tue" / "Wed" / "Thu" / "Fri"
                        / "Sat" / "Sun"
       month        =   "Jan" / "Feb" / "Mar" / "Apr" / "May"
                        / "Jun" / "Jul" / "Aug" / "Sep"
                        / "Oct" / "Nov" / "Dec"
       day          =   1*2DIGIT
       time         =   1*2DIGIT ":" 1*2DIGIT [ ":" 1*2DIGIT ]
       timezone     =   ( "+" / "-" ) 4DIGIT
       year         =   ( 4DIGIT / 2DIGIT )

       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, dailight saving time.

       Example:

        From roessler@does-not-exist.org Fri Jun 23 02:56:55 2000

       In order to avoid mis-interpretation of lines  in  message
       bodies  which  begin with the four characters "From", fol-
       lowed by a space character, the character ">" is  commonly
       prepended in front of such lines.

LOCKING
       Since  mbox files are frequently accessed by multiple pro-
       grams in parallel, mbox  files  should  generally  not  be
       accessed without locking.

       Three   different  locking  mechanisms  (and  combinations
       thereof) are in general use:

       o      fcntl(2) locking is mostly used on  recent,  POSIX-
              compliant  systems.  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.

       o      flock(2)  locking  is mostly used on BSD-based sys-
              tems.

       o      Dotlocking is used on all  kinds  of  systems.   In
              order  to lock an mbox file named folder, an appli-
              cation 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)  sys-
              tem 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 variants of the fcntl(2)  and
       flock(2) sytem 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 individ-
       ual 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. Failure to do so may result in loss of e-mail data,
       and in corrupted mbox files.

FILES
       /var/spool/mail/user
              user's incoming mail folder.

       ~user/mbox
              user's  archived  mail messages, in his home direc-
              tory.

       ~user/Mail/
              A directory in user's home directory which is  com-
              monly used to hold mbox format folders.

SEE ALSO
       elm(1),  fcntl(2),  flock(2),  link(2), local(8), mail(1),
       maildir(5),   mail.local(8),   mutt(1),   mutt_dotlock(1),
       pine(1), procmail(1), sendmail(8)

       D.  Crocker, Standard for the format of ARPA Internet text
       messages, RFC 822

       M. R. Horton, UUCP mail interchange format  standard,  RFC
       976

AUTHOR
       The  present  document  was  written  by  Thomas  Roessler
       .

HISTORY
       The mbox format occured in Version 6 AT&T Unix.

       A variant of this format was documented in RFC 976.



Unix                       August 2000                    mbox(5)