post-mode is an emacs major mode. If you use emacs as your text editor with the mutt mail client then you should use post-mode to make your life easier.

The Woodnotes Guide to the Mutt Email Client

Muttprint formats the output of mail clients to a good-looking printing. It uses the typesetting system LaTeX, which is normally part of every Linux distribution and which is also available for other operating systems like *BSD and Solaris.

IMAPFilter is a mail filtering utility. It connects to remote mail servers
using the Internet Message Access Protocol (IMAP), sends searching queries to
the server and processes mailboxes based on the results. It can be used to
delete, copy, move, flag, etc. messages residing in mailboxes at the same or
different mail servers. The 4rev1 and 4 versions of the IMAP protocol are
supported.

KBiff is a "biff" or new mail notification utility. It is highly configurable but very easy to use and setup. It tries to combine the best of the features of most of the "other" biff programs out there.

Mutt is a small but very powerful text-based mail client for Unix operating systems.