Post Office Protocol
RFC 1939 - Post Office Protocol - Version 3
RFC 1734 - POP3 AUTHentication command (RFC 5034で改訂)
RFC 1725 - Post Office Protocol - Version 3 (RFC 1939で改訂)
RFC 1460 - Post Office Protocol - Version 3 (RFC 1725で改訂)
RFC 1225 - Post Office Protocol - Version 3 (RFC 1460で改訂)
RFC 1081 - Post Office Protocol - Version 3 (RFC 1225で改訂)
RFC 937 - POST OFFICE PROTOCOL - VERSION 2
RFC 918 - POST OFFICE PROTOCOL (RFC 937で改訂)