mddiff - computes diff for maildirs
  mddiff [--max-mailno mno] [--db-file dbf] [-l|--list] [-s|--symlink]
         [--exclude globexpr] [-v|--verbose] [-d|--dry-run] 
         [-n|--no-delete] [--help] [--sha1sum] paths
  mddiff computes the delta from an old status of a maildir (previously
  recorded in a support file, called db file) and the current status, 
  generating a set of commands (a diff) that a third party software can 
  apply to synchronize a (eventually remote) copy of the maildir.

  If paths is a single file name, and that file is a fifo, mddiff reads
  from it file names separated by new line and outputs the sha1 of its header
  and body separated by space.

      $ mddiff /tmp/fifo_for_mddiff 
      806a0ffe4f29766effd764... 463e543da9dac8e298...
      582cbb6a5cd3ce13965c8c... 8fa60a7458b1157193...

  If paths is a single file name, and that file is a fifo, and the -s option
  is passed, mddiff reads from that fifo two lines at a time, respectively
  a source name and a target name. It then creates a symlink named as
  as the target name pointing to the source name. If some dictories need to be
  created in order to create the symlink, this is also done. mddiff will
  print 'OK' on stdout to signal a success, 'ERROR' to signal an error.
  If paths is a list of directories, mddiff outputs a list of actions a client
  has to perform to synchronize a copy of the same maildirs. This set of actions
  is relative to a previous status of the maildir stored in the db file.
  The input directories are traversed recursively, and every file encountered
  inside directories named cur/ and new/ is a potential mail message (if it 
  contains no \\n\\n it is skipped).

      $ mddiff ~/Mail/
      ADD ~/Mail/cur/1239038050.14937_1.garfield:2,S 66532ebb05b252e... 
  Every client (endpoint using mddiff for synchronization) must use a different
  db-file, and the db-file is strictly related with the set of directories given
  as arguments, and should not be used with a different directory set. Adding
  items to the directory set is safe, while removing them may not do what you
  want (delete actions are generated).

  mddiff does not alter the dbf file, it generates a new one called
  It is up to the higher level tool smd-server(1) to rename to dbf 
  in case the other endpoint successfully applied the diff.

  The --exclude option tells mddiff to ignore all paths matching the given
  glob(7) expression. This option can be passed multiple times. Matching
  is performed using fnmatch(3) with no special flags, thus '*' and '?' match
  any character including '/'. Matching is performed when a directory is
  entered. If the match is successful, the directory and all its 
  subedirectories are skipped.

  The --no-delete option tells mddiff to not output a DELETE action for
  files that disappear. Note that a DELETE action is anyway generated for
  files that are moved (i.e. move is COPY plus DELETE). The result is that
  deletions are not propagated to the other endpoint.

  --max-mailno mno      Estimation of max mail message number (defaults to the
                        number of messages in the db-file + 1000 or 500000
                        if there is no db-file). You may want to decrease it
                        for the first run on small systems. It is anyway
                        increased automatically when needed
  --db-file dbf         Name of the cache for the endpoint (default db.txt)
  --exclude globexpr    Exclude paths maching the given expression
  --sha1sum             Behaves like the sha1sum utility
  --mkdir-p             Behaves like mkdir -p
  --mkfifo              Behaves like mkfifo
  -l --list             Only list the mailboxes recursively contained in paths
  -s --symlink          Create symlinks for paths read on the input fifo
  -v --verbose          Increase program verbosity (printed on stderr)
  -d --dry-run          Do not generate a new db-file
  -n --no-delete        Do not track deleted files
  --help                This help screen

  mddiff is a low level utility, used by smd-server and smd-client. You
  should use higher level tools like smd-pull(1), smd-push(1) and smd-loop(1)

  smd-client(1), smd-server(1), smd-pull(1), smd-push(1), smd-loop(1)