Simple Mail Transfer Protocol - technical definition

Email is sent with this protocol, as defined in RFC 821. SMTP has been assigned port 25. If someone knows this information, he or she can use telnet to directly connect to any email server worldwide and send email. The only tools necessary to do this are a telnet client program (included in any operating system supporting TCP/IP, which basically means all modern ones) and a recipientÂ’s email address. Email programs, text editors, and browsers are not needed.

See Also: Electronic Mail or Email; Port and Port Numbers; TCP/IP or Transmission Control Protocol/Internet Protocol.