Mmh is a modified version of the electronic mail handling system nmh.
Nmh (new MH) itself was originally based on the package MH-6.8.3, and
was intended to be a (mostly) compatible drop-in replacement for MH.
In contrast, mmh is not intended to be a drop-in replacement for nmh,
but rather aims for the modernization and simplification of nmh,
accepting reduced compatiblity if it, at the same time, allows to
achieve greater goals from mmh's point of view.

WWW: http://marmaro.de/prog/mmh/