(MMDF) An electronic mail system for Unix(?) which is much easier to configure than sendmail. The source is available.

MMDF is a versatile and configurable mail routing system (mta) which also includes user interface programs (mua). It can be set up to route mail to different domains and hosts over different channels (e.g. smtp, uucp). On unix systems, its configuration begins with the /usr/mmdf/mmdftailor file, which defines the machine and domain names, various other configuration tables (alias, domain, channel) and other configuration information.