There are several basic methods of reading and sending mail. Each has its advantages and disadvantages.
Mail is the traditional unix mail command.
It is a single program with its own set of commands which are executed from within. Both elm and pine provide a unified, easy to use interface. MH is the Message Handler. It is a collection of smaller programs each invoked independantly from unix and each performing an essential function for mail processing. This guide is not an exhaustive manual on any of the mail systems.