15.6 POP3
Post Office Protocol version 3 (POP3) is a simple protocol that users can use to download emails from their mailbox on the mail server to local mailboxes on their PC. It is intended to work offline with the mail server. POP3 is specified in RFC 1939.
A client establishes connection with the well-known TCP port 110 of a server. After this connection has been established, the server introduces itself, and is in the Authentication state (i.e., waiting for an authentication from its user). For example:
+ OK QPOP (version 2.1.4-R4-b5a) at t1.pvt.cz starting <3774.978040846@t1.pvt.cz>
Basic authentication is done with a username and password. If authentication is valid, communication proceeds to the Transaction state, where clients can work ...
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