What is the Simple Mail Transfer Protocol (SMTP)?

Simple Mail Transfer Protocol (SMTP) is the de facto standard for electronic mail transport across the Internet. When you send an email message, SMTP packages your message in a kind of envelope and relays it to its destination. Multiple servers are often involved in the transport of the message, and as it passes through them, each one time-stamps and tags it. Thus, when the message arrives, the recipient can get an idea of where it's been, and when it was sent. SMTP also handles error messages, sending notifications to senders when there is difficulty delivering their mail.

When you set up a POP mail or IMAP client, such as Eudora or Outlook Express, you must specify an SMTP server for your outgoing mail. This may be different from the server you use to check incoming mail.

The SMTP server for all Indiana University campuses except IPFW (which uses the POP protocol and its own SMTP servers), is:

Note: IU's outbound (SMTP) server requires authentication and a secure connection (SSL or TLS). Make sure you enable these settings in your mail software. For more information, see Instructions for changing mail settings to meet UITS requirements.

SMTP was introduced in a series of RFCs, notably 772, 780, and 788, with the current base specification appearing in 1982's RFC 821 at:

Work continues on SMTP, however, and over the years its capabilities have been significantly enhanced. Modern programs that implement SMTP, such as sendmail, are based on these Extended SMTP (ESMTP) standards.

For more information, visit the moderated newsgroup info.ietf.smtp.

Also see:

• Where can I find a list of standard TCP port designations?
• What is DNS?
• What is an SMTP server?
• At IU, for my departmental server, how do I request exemption from the SMTP authentication requirement?
• At IU, if I use an outside ISP, what should I know about my outgoing mail server?
• At IU, what SMTP (outgoing mail) server should I specify when configuring my IMAP mail software?