Post Office Protocol

Post Office Protocol (POP) is a protocol designed to allow single-user computers to retrieve electronic mail from a POP server via TCP/IP. The default port is 110.

Description
The POP server might be a computer with a permanent Internet connection, whereas its clients might only connect to it occasionally, e.g. by modem. As of 1994, there were three versions: POP, POP2, and POP3. Later versions are not necessarily compatible with earlier ones.