What is SMTP?

SMTP stands for Simple Mail Transport Protocol. SMTP is a TCP/IP protocol governing electronic mail transmission and reception. The details of SMTP are in RFC 821 of the Internet Engineering Task Force (IETF).

SMTP (Simple Mail Transfer Protocol) is a TCP/IP protocol used in sending and receiving e-mail. However, since it is limited in its ability to queue messages at the receiving end, it is usually used with one of two other protocols, POP3 or IMAP, that let the user save messages in a server mailbox and download them periodically from the server. In other words, users typically use a program that uses SMTP for sending e-mail and either POP3 or IMAP for receiving e-mail. 
SMTP usually is implemented to operate over Internet port 25. An alternative to SMTP that is widely used in Europe is X.400.

See Also

Simple Mail Transfer Protocol