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.
Many years ago, a proposal was outlined for a POP4 specification, complete with a working server implementation. The proposed POP4 extension adds basic folder management, multipart message support, as well as message flag management, allowing for a light protocol which supports some popular IMAP features which POP3 lacks. No progress has been found in the POP4 specification since 2003.
- RFC 1939 – Post Office Protocol - Version 3 (STD 53)
- RFC 1957 – Some Observations on Implementations of the Post Office Protocol (POP3)
- RFC 2195 – IMAP/POP AUTHorize Extension for Simple Challenge/Response
- RFC 2384 – POP URL Scheme
- RFC 2449 – POP3 Extension Mechanism
- RFC 2595 – Using TLS with IMAP, POP3 and ACAP
- RFC 3206 – The SYS and AUTH POP Response Codes
- RFC 5034 – The Post Office Protocol (POP3) Simple Authentication and Security Layer (SASL) Authentication Mechanism
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