Programming Internet Email

MH

The MH Mail Handling System is a powerful open source package for handling electronic mail on Unix systems. It provides command-line utilities for all aspects of mail, including POP, IMAP, and MIME support. Several user graphical interface packages are available for MH. A recently rewritten version, nmh, is supposedly cleaner and easier.

The MH mailbox format is used by MH and nmh. Instead of appending multiple messages to a single file like mbox, MH mailboxes consist of a directory where each message is contained within its own file.

The filename of each message corresponds to its message number. When a message is deleted, ^[12] its name is prepended with a literal comma. For example, a message named “45” would be renamed to “,45” when marked for deletion.

If we look at a directory listing for a bunch of MH mailboxes, we might see something like this:

[lovelace]$ pwd
/mnt/home/dwood/mh_mail/Inbox
[lovelace]$ ls -l
total 288
-rw-r-----   1 dwood    dev         84317 Dec 16 17:21 ,4
-rw-r-----   1 dwood    dev        144308 Dec 16 17:10 1
-rw-r-----   1 dwood    dev         37651 Dec 16 17:10 2
-rw-r-----   1 dwood    dev          9764 Dec 16 17:21 3
-rw-r-----   1 dwood    dev         12345 Dec 16 17:38 5

This shows a directory listing for a mailbox called Inbox in MH format. The directory name is the mailbox name, and each message is held in a separate file. Message number 4 has been marked for deletion but has not yet been expunged (permanently deleted).

This type of mailbox solves many problems when compared to the mbox format. Messages may contain ...