Simple Mail Transfer Protocol

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Simple Mail Transfer Protocol (SMTP) is the de facto standard for email transmission across the Internet.

Related Topics:
De facto - Email - Internet

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SMTP is a relatively simple, text-based protocol, where one or more recipients of a message are specified (and in most cases verified to exist) and then the message text is transferred. It is quite easy to test a SMTP server using the telnet program. SMTP uses TCP port 25. To determine the SMTP server for a given domain name, the MX (Mail eXchange) DNS record is used.

Related Topics:
Telnet - TCP - Port - Domain name - MX - DNS

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SMTP started becoming widely used in the early 1980s. At the time, it was a complement to UUCP which was better suited to handle e-mail transfers between machines that were intermittently connected. SMTP, on the other hand, works best when both the sending and receiving machines are connected to the network all the time.

Related Topics:
1980s - UUCP

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Sendmail was one of the first (if not the first) mail transfer agents to implement SMTP. As of 2001 there are at least 50 programs that implement SMTP as a client (sender of messages) or a server (receiver of messages). Some other popular SMTP server programs include Philip Hazel's exim, IBM's Postfix, D. J. Bernstein's qmail, and Microsoft Exchange Server.

Related Topics:
Sendmail - Mail transfer agents - As of 2001 - Philip Hazel - Exim - IBM - Postfix - D. J. Bernstein - Qmail - Microsoft Exchange Server

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Since this protocol started out as purely ASCII text-based, it did not deal well with binary files. Standards such as MIME were developed to encode binary files for transfer through SMTP. Today, most SMTP servers support the 8BITMIME extension, permitting binary files to be transmitted almost as easily as plain text.

Related Topics:
ASCII - MIME - 8BITMIME

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SMTP is a "push" protocol that does not allow one to "pull" messages from a remote server on demand. To do this a mail client must use POP3 or IMAP. Another SMTP server can trigger a delivery in SMTP using ETRN.

Related Topics:
Mail client - POP3 - IMAP - ETRN

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