Post Office Protocol 3 (POP3)

Post Office Protocol 3 (POP3) an IETF standard for the retrieval of email. Under POP3, the default action is to move email from a server to a client and to delete the message from the server. POP3 runs over the well-known TCP port 110. POP3 contrasts in its email retrieval approach with the alternative IMAP4.

See: RFC 1939.

References:

http://www.emailaddressmanager.com/tips/protocol.html

http://www.businesscreatorpro.com/articles/what-is-imap-and-pop3.php