ⓘ Post Office Protocol


ⓘ Post Office Protocol

In computing, the Post Office Protocol version 3 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 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.


1. Related Requests For Comments RFCs

  • RFC 2384 – POP URL Scheme
  • RFC 5034 – The Post Office Protocol POP3 Simple Authentication and Security Layer SASL Authentication Mechanism
  • RFC 1957 – Some Observations on Implementations of the Post Office Protocol POP3
  • RFC 3206 – The SYS and AUTH POP Response Codes
  • RFC 2595 – Using TLS with IMAP, POP3 and ACAP
  • RFC 2195 – IMAP/POP AUTHorize Extension for Simple Challenge/Response
  • RFC 1939 – Post Office Protocol - Version 3 STD 53
  • RFC 2449 – POP3 Extension Mechanism