Glossary definition of Simple Mail Transfer Protocol

Also known as: SMTP

SMTP (Simple Mail Transfer Protocol) is the main protocol used to control the transfer of electronic mail (e-mail) messages on the Internet. SMTP is a TCP / IP protocol, and this specifies the format of the messages, and how servers and terminals are to interact.

SMTP is usually employed only for the sending of the messages, with other protocols used to receive them-e.g. POP3 or IMAP-which can save the messages in a mailbox for download from the server to a particular terminal, as required by the user. ESMTP, the Extended Simple Mail Transfer Protocol, allows multimedia files to be sent as e-mail.