*SMTP* or _Simple Mail Transfer Protocol_ is the protocol used to send and receive email on the internet.

SMTP is simply an ASCII text protocol that goes over port 25, an SMTP server or Mail Transfer Agent such as [[Sendmail]] or [[qmail]] or [[Postfix]] listens on port 25 and text information about an email is exchanged when an is email is sent.

SMTP as a protocol is push based, thus it is quite susceptible to spam. The push nature of SMTP means that other protocols are necessary for intermittently connected email clients: IMAP or POP3.

To exchange information outside of simple ASCII messages, MIME encoding is used to transfer binary files or Unicode encoded messages.