Simple mail transfer protocol (SMTP) is the defacto standard for sending e-mail messages between servers on the Internet and is part of the TCP/IP (transmission control protocol/Internet protocol) protocol suite.
SMTP servers route SMTP messages throughout the Internet to e-mail servers that provide message repositories for incoming mail. The latter use the POP3 (post office protocol) or IMAP4 (Internet message access protocol) access protocol to communicate with users' e-mail client programs.
SMTP was originally designed only for transmitting ASCII plain text messages. However, MIME (multipurpose Internet mail extensions) and other encoding methods were subsequently developed to allow a wide variety of file types (e.g., images, sound and executable programs) to be attached to and transported with e-mail messages.
SMTP began to come into widespread use in the early 1980s as a complement to UUCP (UNIX-to-UNIX copy), a utility that copies files between computers and which was widely used for mail transfers. UUCP is better suited for handling mail transfers between computers that are intermittently connected, whereas SMTP is most suitable when both the sending and receiving computers are continuously connected to the network.
Created November 7, 2005.