.TL
mum \(en modern UNIX mail interface
.AU
John Ankarström
.SH
Introduction
.LP
Mum is a text-based e-mail client for UNIX and UNIX-like operating
systems that supports both plain-text and HTML e-mail.
It introduces a new method for local storage of e-mail, called
indexed mbox.
Furthermore, it uses
.I views
\(en simple scripts that filter messages \(en instead of folders.
.PP
In this document, the fundamental concepts of mum are explained.
.SH
The indexed mbox format
.LP
There are two popular methods for local storage of e-mail on UNIX
systems: mbox and Maildir.
Maildir is a powerful but complicated solution, while mbox is a
simple but inefficient solution.  The "indexed mbox" format introduced
by mum builds on the mboxcl2 format, but enhances it with an
additional file called an
.I index ,
which carries the same name as the mbox plus the extension
.I .i .
The index contains all headers from the mbox file, including the
.I From_
line, without the actual contents of the corresponding messages.
Each block of headers contains an additional header called
.I Offset ,
which contains the position of the corresponding message in the
mbox file, described as a byte offset.
Additionally, a
.I Content-Length
header is included in both mbox and mbox.i.
(Note further that the mbox and mbox.i files are append-only.)
.PP
Mum and its associated view scripts use the index for most operations.
Whenever it is time to read the actual contents of a message, the
message is retrieved from the mbox using the offset specified in
the index.