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What is it?
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nmh (new MH) is an electronic mail handling system - a MUA (Mail
User Agent) package for end-users to handle their e-mail. It was
originally based on the package MH-6.8.3, and is intended to be a
(mostly) compatible drop-in replacement for MH.

nmh consists of a collection of fairly simple single-purpose programs
to send, receive, save, retrieve, and manipulate e-mail messages. Since
nmh is not a single comprehensive program, you may freely intersperse
nmh commands with other shells commands, or write custom scripts which
utilize these commands in flexible ways.

WWW: http://savannah.nongnu.org/projects/nmh/