POP3, full name "Post Office Protocol - Version 3", or "Post Office Protocol version 3." Is the TCP / IP protocol suite, a member of the RFC 1939 definition. The protocol used to support remote management using a client e-mail on the server. SSL encryption provides a POP3 protocol is called POP3S. POP protocol support "offline" mail processing. The specific process is: message is sent to the server, e-mail client program called a mail client to connect to the server and download all unread e-mail. The offline access mode is a store and forward service, the message from the mail server to the personal terminal machine, generally PC, or MAC. Once the message is sent to a PC, or MAC, the mail server the mail will be deleted. However, most of the current POP3 mail server can "only download messages, the server does not delete", which is to improve the POP3 protocol.