{
    "mode": "man",
    "parameter": "mmdf",
    "section": "5",
    "url": "https://www.chedong.com/phpMan.php/man/mmdf/5/json",
    "generated": "2026-06-16T10:00:01Z",
    "sections": {
        "NAME": {
            "content": "MMDF - Multi-channel Memorandum Distribution Facility mailbox format\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "This document describes the MMDF mailbox format used by some MTAs and MUAs (i.e.  scomail(1))\nto store mail messages locally.\n\nAn MMDF mailbox is a text file containing an arbitrary number of e-mail messages.  Each  mes‐\nsage  consists  of  a postmark, followed by an e-mail message formatted according to RFC822 /\nRFC2822, followed by a postmark. The file format is line-oriented.  Lines  are  separated  by\nline  feed  characters (ASCII 10). A postmark line consists of the four characters \"^A^A^A^A\"\n(Control-A; ASCII 1).\n\nExample of a MMDF mailbox holding two mails:\n\n^A^A^A^A\nFrom: example@example.com\nTo: example@example.org\nSubject: test\n\n>From what I learned about the MMDF-format:\n^A^A^A^A\n^A^A^A^A\nFrom: example@example.com\nTo: example@example.org\nSubject: test 2\n\nbar\n^A^A^A^A\n\nIn contrast to most other single file mailbox formats like MBOXO  and  MBOXRD  (see  mbox(5))\nthere  is no need to quote/dequote \"From \"-lines in MMDF mailboxes as such lines have no spe‐\ncial meaning in this format.\n\nIf the modification-time (usually determined via stat(2))  of  a  nonempty  mailbox  file  is\ngreater  than the access-time the file has new mail. Many MUAs place a Status: header in each\nmessage to indicate which messages have already been read.\n",
            "subsections": []
        },
        "LOCKING": {
            "content": "Since MMDF files are frequently accessed by multiple programs in parallel, MMDF files  should\ngenerally not be accessed without locking.\n\nThree different locking mechanisms (and combinations thereof) are in general use:\n\n•      fcntl(2)  locking is mostly used on recent, POSIX-compliant systems. Use of this lock‐\ning method is, in particular, advisable if MMDF files are accessed through the Network\nFile  System  (NFS),  since  it seems the only way to reliably invalidate NFS clients'\ncaches.\n\n•      flock(2) locking is mostly used on BSD-based systems.\n\n•      Dotlocking is used on all kinds of systems. In  order  to  lock  an  MMDF  file  named\nfolder, an application first creates a temporary file with a unique name in the direc‐\ntory in which the folder resides. The application then tries to use the link(2) system\ncall to create a hard link named folder.lock to the temporary file. The success of the\nlink(2) system call should be additionally verified using stat(2) calls. If  the  link\nhas  succeeded,  the  mail folder is considered dotlocked. The temporary file can then\nsafely be unlinked.\n\nIn order to release the lock, an application just unlinks the folder.lock file.\n\nIf multiple methods are combined, implementors should make sure to use the non-blocking vari‐\nants of the fcntl(2) and flock(2) system calls in order to avoid deadlocks.\n\nIf  multiple  methods are combined, an MMDF file must not be considered to have been success‐\nfully locked before all individual locks were obtained. When one of  the  individual  locking\nmethods  fails, an application should release all locks it acquired successfully, and restart\nthe entire locking procedure from the beginning, after a suitable delay.\n\nThe locking mechanism used on a particular system is a matter of local policy, and should  be\nconsistently  used by all applications installed on the system which access MMDF files. Fail‐\nure to do so may result in loss of e-mail data, and in corrupted MMDF files.\n",
            "subsections": []
        },
        "CONFORMING TO": {
            "content": "MMDF is not part of any currently supported standard.\n",
            "subsections": []
        },
        "HISTORY": {
            "content": "MMDF was developed at the University of Delaware by Dave Crocker.\n",
            "subsections": []
        },
        "SEE ALSO": {
            "content": "scomail(1), fcntl(2), flock(2), link(2), stat(2), mbox(5), RFC822, RFC2822\n\n",
            "subsections": []
        },
        "AUTHOR": {
            "content": "Urs Janssen <urs@tin.org>\n\n\n\nUnix                                     February 18th, 2002                                 mmdf(5)",
            "subsections": []
        }
    },
    "summary": "MMDF - Multi-channel Memorandum Distribution Facility mailbox format",
    "flags": [],
    "examples": [],
    "see_also": [
        {
            "name": "scomail",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/scomail/1/json"
        },
        {
            "name": "fcntl",
            "section": "2",
            "url": "https://www.chedong.com/phpMan.php/man/fcntl/2/json"
        },
        {
            "name": "flock",
            "section": "2",
            "url": "https://www.chedong.com/phpMan.php/man/flock/2/json"
        },
        {
            "name": "link",
            "section": "2",
            "url": "https://www.chedong.com/phpMan.php/man/link/2/json"
        },
        {
            "name": "stat",
            "section": "2",
            "url": "https://www.chedong.com/phpMan.php/man/stat/2/json"
        },
        {
            "name": "mbox",
            "section": "5",
            "url": "https://www.chedong.com/phpMan.php/man/mbox/5/json"
        }
    ]
}