Simple Mail Transfer Protocol


(SMTP) A protocol defined in STD 10, RFC 821, used to transfer electronic mail between computers, usually over Ethernet. It is a server to server protocol, so other protocols are used to access the messages. The SMTP dialog usually happens in the background under the control of the message transfer agent, e.g. sendmail but it is possible to interact with an SMTP server using telnet to connect to the normal SMTP port, 25. E.g.

 telnet 25

You should normally start by identifying the local host:


You can then issue commands to verify an address or expand an alias:

 VRFY [email protected]
 VRFY postmaster

or expand a mailing list:

 EXPN c-help

You can even send a message:

 MAIL From:<[email protected]>
 RCPT To:<[email protected]>
 What is the point?

This is useful if you want to find out exactly what is happening to your message at a certain point.

See also Post Office Protocol, RFC 822, sendmail.

Last updated: 1995-10-17

Nearby terms:

Simple Gateway Control ProtocolSimple Mail Transfer Protocolsimple multicast protocol

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