SMTP

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SMTP

Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail transmission. First defined in RFC 821 in 1982, it was last updated in 2008 with RFC 5321. SMTP is used by mail servers to send and receive outgoing mail via port 25, while mail submission typically uses port 587.

History

SMTP was developed as part of the early ARPANET. The original specification by Jon Postel introduced a simple text-based protocol. Over time, extensions like ESMTP added authentication and binary attachments.

Features

• Uses plain text commands like HELO, MAIL FROM, RCPT TO, DATA
• Supports relaying between Mail Transfer Agents
• Often combined with POP3 or IMAP for retrieval
• Security can be added via STARTTLS or SMTP-AUTH

See also

• Email
• Mail server