MMDF Users Group

MMDF project page

This page contains information relating to the Multi-channel Memo Distribution Facility (MMDF). MMDF is a freely distributable Internet "Mail Transfer Agent (MTA)" written in C that runs on various flavours of UNIX. Mail Transfer Agents are the software that moves electronic mail among hosts and servers on the Internet and over other kinds of networks (e.g. UUCP).

MMDF is the standard mail system on SCO UNIX, but is not as widely deployed as some other MTAs, such as Sendmail. This is mostly because BSD UNIX included Sendmail as the standard mail system. It might partly be caused by the larger number of configuration files with MMDF.

The MMDF Users Group is an ad hoc set of folks who use MMDF for mail transfer, cooperate on advancing/improving MMDF, and cooperate on advancing/improving the documentation for MMDF. Membership in the MMDF Users Group is not well defined at present and probably is the same as the set of folks on the MMDF mailing list (see below).

NOTE: The links here go to selected documents and software at various other web/ftp sites on the Internet. Most content is not local to this server.

MMDF Feature Highlights:


User-level Mail Sorting: MMDF uses the .maildelivery file in the user's home directory for automatic sorting and delivery control for incoming messages.

Dynamic Log/Debug Configuration: The MMDF administrator can adjust the logging/debugging levels without stopping and restarting the mail delivery processes.

Mail blocking: MMDF can filter email to block transmission of undesirable ("spam") mail based on where the mail came from, how it arrived here, and where it is going. Spam blocking is enabled by default.

Modular design: it is easy to add new transport or translation channels for special email gateways and its easy to understand how the existing channel software works.

High-capacity: Unlike some other systems (e.g. Sendmail), MMDF is designed to process very very large message flows and handle very large message queues efficiently.

Secure Design: MMDF is the only widespread MTA designed using the Principle of Least Privilege. Nearly all of MMDF runs as an unprivileged user (not as root), so it is significantly less of a security risk than nearly any other mail transfer agent. It also performs numerous run-time permission checks and other security checks to ensure everything is configured securely. Many sites have converted to MMDF so they won't have to patch the security hole-of-the-month common with some other mailers.

NEW FEATURES (as of Patch Level 44)

Significantly enhanced portability

8-bit clean mail transer

Support for header lines longer than 256 characters

More detailed information in the "Received:" line of the header

Increased Spam resistance

Easier compile-time configuration due to GNU configure support

Compile-time option to support NIS/NIS+

Compile-time option to support TCP Wrappers

Compile-time option to support IdentD

Compile-time option for mail relaying, which defaults to OFF for SPAM avoidance.

Support for GNU gdbm in addition to ndbm and dbm.

MMDF & Related Documentation

Most are in HTML format. Some in ASCII format.

Standard MMDF

Addressing in MMDF-II by Steve Kille.

Authorisation & Accounting in Store & Forward Message Handling Systems by D.H. Brink & S.E. Kille.

Configuring MMDF Authorisation from the standard MMDF distribution.

Installing & Operating MMDF-II by Douglas P. Kingston III, Steve Kille, Julian Onions, Daniel B. Long from the standard MMDF distribution.

MMDF-II: A Technical Review by Douglas P. Kingston III from Proceedings of the 1984 Summer USENIX Conference, Salt Lake City, UT, June 1984, pp. 32-41.

MMDF Frequently Asked Questions maintained by Jerry Sweet of Irvine Compiler.

Supplement to the MMDF Frequently Asked Questions maintained by Jerry Sweet of Irvine Compiler.


Configuring MMDF in a TCP/IP Environment by Christopher Durham (SCO). Part of the SCO UNIX MMDF Documentation, but also useful for standard MMDF administrators.

Configuring MMDF in a UUCP Environment by Christopher Durham (SCO). Part of the SCO UNIX MMDF Documentation, but also useful for standard MMDF administrators.

MMDF Software Distribution

MMDF Patch Level 44 is the official current MMDF release. The MMDF archives are available from Univ. Kaiserslauten, Germany via http or ftp. The latest official release is mmdf-2.44-final available from the above ftp site.

The MMDF PL44 software should work under any modern POSIX-compliant operating system with a modern C compiler. Most folks seem to use the GNU C compiler, though other compilers are known to work. MMDF 2.44 has been specifically tested and is known to work on these systems:

  • FreeBSD 3.x (Intel)
  • HPUX 9.05 (PA-RISC)
  • HPUX 10.20 (PA-RISC)
  • Linux Debian (Intel)
  • Linux RedHat 4.2 (Intel)
  • Linux RedHat 5.1 (Intel)
  • OpenBSD (Intel)
  • SunOS 4.1.4 (SPARC)
  • Solaris 2.4 (SPARC)
  • Solaris 2.51 (SPARC)
  • Solaris 2.6 (SPARC)
  • Numerous bug fixes and enhancements are present in this new MMDF version. A security fix for smtpd is also present in the MMDF 2.44 release. Thanks to Kai Krueger and the others there for putting this new release together !

    Older MMDF releases exist, but are outdated and should not be used. In particular, the MMDF software archives online at,, and their mirror sites around the world are out of date.

    Mail User Agents that support MMDF

    Elm is a popular mail user agent for UNIX. It uses a curses-style text windowing system that works not only with xterms, but also on ordinary terminals. Originally from HP, Elm is now maintained by a public set of developers operating in the manner of a trust. It has a compile-time option to support MMDF-style mailboxes. Freely Distributable.

    Exmh is an X11 GUI variant of MH. Exmh is written in Tcl/Tk. It was developed and is maintained by Brent Welch at Sun Microsystems Laboratories. The original MH package itself is described below. Freely distributable.

    IMAP-4 Toolkit from Mark Crispin at the University of Washington includes support for MMDF mailboxes and adding an IMAP-4 server to an MMDF system. Freely Distributable.

    MH is originally from The RAND Corporation and is presently maintained at UC Irvine. MH is a shell/command-line toolset that runs on many versions of UNIX and supports both Sendmail and MMDF. One should be sure to obtain version 6.8.3 or later of MH if one is going to install it. Xmh is a fast X11 GUI front-end for MH. Freely Distributable.

    Mail User's Shell (MUSH) is a command-line mail user agent for UNIX and DOS that supports both Sendmail and MMDF. It is popular with folks familiar with UCB Mail and those connected to their UNIX system via slow dialup lines. This product was the basis for the commercial Z-Mail for UNIX product. Users should probably apply the patches located in the Contrib subdirectory to the base 7.2.5 distribution. Freely distributable.

    Mutt is another mail user agent. It supports MMDF, UCB Mail, and other mailbox formats. It is popular in some parts of the Linux community.

    Pine is a simple mail user agent for UNIX developed at the University of Washington. Pine supports TENEX-style, MMDF-style, and Sendmail-style mailbox formats. Freely distributable.

    Z-Mail for UNIX is the commercial derivative of MUSH. It supports both command-line and X11 GUI interfaces and runs on most commercial versions of UNIX. It is bundled with SGI IRIX, where it is called MediaMail. It supports both MMDF-style and UCB-style mailbox formats and automatically detects which is being used for a given mailbox file. NB: The Z-Mail for Windows product appears to be unrelated to Zmail for UNIX. Commercial product.

    Miscellaneous Software

    MMDF Administrative Utilities written by John DuBois for SCO UNIX but generally portable to other flavours of UNIX. These are not part of the standard MMDF distribution. Freely distributable.

    Procmail is another mail sorting program. It is different from the mail sorting built-in to MMDF and might be useful to some folks. It claims to be MMDF compatible. Freely Distributable.

    MajorDomo is a very popular automated mailing list administration package written in PERL. It works with MMDF 2.44 without patching. See the MMDF FAQ for more details.

    TIN is a NNTP newsreader for UNIX. It supports saving news into MMDF-format mailboxes by setting an environment variable. Freely Distributable.

    Other Resources

    Jerry Sweet's MMDF web site at Irvine Compiler has a lot more information on MMDF.

    Mark Vasoll's MMDF web site at C2 Technology also has a lot more information on MMDF. A number of the above documents are available here in Postscript format.

    There is also an open MMDF mailing list hosted by Mark Vasoll at C2 Technology. This list is low-volume, very polite, and has a good signal/noise ratio. If you post, please respect the other list readers. Subscribe to it by sending an email request to

    Credits: Most of the information on this page is derived directly from the MMDF FAQ maintained by Jerry Sweet. Thanks to him for creating and maintaining the MMDF FAQ. Thanks to The Inner Net for hosting this site. This page was last updated 17 May 2001 by kkrueger. Suggestions for change/improvement should be sent via email to rja or kkrueger.