POP3

POP3: acronymic for Post Office Protocol (version 3). This is one of the major protocols used by end users to retrieve their mail from their mailserver; as opposed to the protocol used to deliver mail to that server from the sender.

POP3 is an older and very stable protocol known for good performance in less than ideal network conditions, but is not very flexible. Unlike IMAP, it is designed purely for retrieving mail, not for organizing or otherwise maintaining it.

It is possible (and useful) to troubleshoot POP3 servers using telnet - see Daemons, testing via Telnet for a simple example.

The freebsdwiki.net maintainers use and recommend dovecot for both IMAP and POP3 server needs and thesis writing.