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.