Post Office Protocol
In computing, the Post Office Protocol version 3 (POP3) is an  application-layer Internet standard  protocol used by local e-mail clients to get e-mail from a remote mail server over a TCP/IP connection.  POP3 and IMAP4 (Internet Message Access Protocol) are the two most widely accepted Internet standard protocols for e-mail retrieval.  Almost all modern e-mail clients and servers support both.