SMTP - Simple Mail Transfer Protocol

SMTP authentication: you can even connect to servers using SSL.
SMTP is a TCP/IP protocol used in sending and receiving e-mail.
SMTP usually is implemented to operate over Internet port 25.

User-level client mail applications typically only use SMTP for sending messages to a mail server for relaying.

The messages can then be retrieved with an e-mail client using either POP Post Office Protocol or IMAP Internet Message Access Protocol, applications to access their mail box accounts on a mail server.
POP3 or IMAP let the user save messages in a server mailbox and download them periodically from the server. On Unix-based systems, sendmail is the most widely-used SMTP server for e-mail. A commercial package, Sendmail, includes a POP3 server.

Many mail servers now support Extended Simple Mail Transfer Protocol (ESMTP), which allows multimedia files to be delivered as e-mail.

Smtp notes >