mail user agent

(MUA) The program that allows the user to compose and read electronic mail messages. The MUA provides the interface between the user and the Message Transfer Agent. Outgoing mail is eventually handed over to an MTA for delivery while the incoming messages are picked up from where the MTA left it (although MUA's running on single-user machines may pick up mail using POP).

Popular MUAs for Unix include elm, mush, pine, and RMAIL.