nmh -- A capable mail handling system with a command line interface.
http://savannah.nongnu.org/projects/nmh
Nmh is an email system based on the MH email system and is intended to
be a (mostly) compatible drop-in replacement for MH. Nmh isn't a single
comprehensive program. Instead, it consists of a number of fairly simple
single-purpose programs for sending, receiving, saving, retrieving and
otherwise manipulating email messages. You can freely intersperse nmh
commands with other shell commands or write custom scripts which utilize
nmh commands. If you want to use nmh as a true email user agent, you'll
want to also install exmh to provide a user interface for it--nmh only
has a command line interface.