MH Message Handling System

The MH Message Handling System is a free, open source e-mail client. It is different from almost all other mail reading systems in that, instead of a single program, it is made from several different programs which are designed to work from the command line provided by the shell on Unix-like operating systems. Another difference is that rather than storing multiple messages in a single file, messages each have their own separate file in a special directory. Taken together, these design choices mean that it is very easy and natural to script actions on mail messages using the normal shell scripting tools. A descendant of MH continues to be developed under the name of nmh.

Design

MH is made up of separate programs such as show, to view a message, scan, to see message titles and rmm to remove messages. By using the pick program, it is possible to select messages, based on sender for example, which the other programs act on. Because the different programs are run separately and at different times, communication between them has to be arranged specially. Information such as the mail which is currently selected is stored in files (in this case .mh_profile in the user's own directory).

MH follows the unix philosophy of "write programs that do one thing and do it well. Write programs to work together. Write programs to handle text streams, because that is a universal interface" (Doug McIlroy).

History

MH was proposed by R Stockton Gaines and Norman Shapiro and developed by Bruce S. Borden at RAND Corporation. Subsequently development was taken over by Marshall T. Rose and John L. Romine working at University of California, Irvine. The last release of MH was 6.8.4 which was a maintenance patch for the 6.8.3 release.

nmh, which is the current active version of MH, was forked from version 6.8.3 of MH. It actually removed some features such as the POP daemon but also improved others such as MIME support. The most recent release of nmh is version 1.2.

MH is in the public domain nmh is released under the BSD Licence.

Performance

The performance of MH is very much dependent on the file system and other features of the operating system that it runs on. Every read of a mail will require starting a separate program, a directory scan in a large directory and a file open before the data can even be accessed. On the other hand, mailbox formats such as mbox which use a single file often require insertion or removal of data in the middle of the file when mails are read or altered and this can be a very slow procedure. In these cases MH will be much faster. With a modern file system designed for large directories and small files such as ReiserFS the performance of MH can be comparable to that of a database based mail storage system.

Graphical interfaces

MH is inherently a command line based system, which limits its marketability to some extent, but also may not always be ideal for viewing emails with graphical content. For these reasons, among others, many users want to have a graphical interface which can also read their MH mailbox. The original program for this purpose was xmh, an X Window System application. After development of xmh ceased, a similar tool called [http://www.exmh.org/ exmh] was developed in Tcl/Tk. Exmh is considered feature-complete and since 2004 there has been little development beyond bug fixes. An open source Emacs interface to MH is provided by the [http://mh-e.sourceforge.net MH-E] project. In addition to these dedicated MH clients, support for MH mailboxes is included in several other clients such as Claws Mail, Novell Evolution and Sylpheed.

ee also

*mbox
*maildir

External links

* [http://www.ics.uci.edu/~mh/ the (old) MH homepage]
* [http://www.nongnu.org/nmh/ the current nmh homepage]
* [http://www.exmh.org/ exmh] an MH front end in Tcl/Tk
* [http://mh-e.sourceforge.net/ MH-E] an Emacs front end to MH