SMTP (Simple Mail Transfer Protocol) is aprotocol used to send a new email. LikePOP andNNTP, it is astate machine-driven protocol.

The protocol is relatively straightforward. Primary complications include supporting various authentication mechanisms (GSSAPI,CRAM-MD5,NTLM, MSN, AUTH LOGIN, AUTH PLAIN, etc.), handling error responses, and falling back when authentication mechanisms fail (e.g., the server claims to support a mechanism, but doesn't).

See also

• SMTP (Wikipedia)
• Related glossary terms:
  • NNTP
  • POP
  • protocol
  • state machine