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 mhs-relay.ac.uk 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@example.com VRFY postmaster
or expand a mailing list:
You can even send a message:
RCPT To: DATA What is the point? . QUIT
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.