Post Office Protocol - Version 3
The Post Office Protocol - Version 3 (POP3) is intended to permit a workstation to dynamically access a maildrop on a server host in a useful fashion. [STANDARDS-TRACK]
Replaces RFC 1081: Post Office Protocol: Version 3, RFC 1225: Post Office Protocol: Version 3, RFC 1460: Post Office Protocol - Version 3, RFC 1725: Post Office Protocol - Version 3.
This document is current and has been amended. 4 later RFCs have changed part of it. Nothing on the RFC itself tells you this.
What it is
POP3: downloading mail from a server, usually deleting it as it goes.
What it solves
Users needed to read mail on a machine that is not the server and is not always connected.
What it means to operate
Still current, still widely deployed, and the source of the recurring support case where mail vanishes from the server because a client is configured to delete on retrieval. IMAP is the answer for anyone with more than one device.
Normative requirements
Every sentence in this RFC carrying an RFC 2119 keyword, with the section it came from.
3 Basic Operation
- MUSTServers MUST send the "+OK" and "-ERR" in upper case.
- MUSTA server MUST respond to an unrecognized, unimplemented, or syntactically invalid command by responding with a negative status indicator.
- MUSTA server MUST respond to a command issued when the session is in an incorrect state by responding with a negative status indicator.
- MAYA POP3 server MAY have an inactivity autologout timer.
- MUSTSuch a timer MUST be of at least 10 minutes' duration.
6 The UPDATE State
- MUSTIf a session terminates for some reason other than a client-issued QUIT command, the POP3 session does NOT enter the UPDATE state and MUST not remove any messages from the maildrop.
7 Optional POP3 Commands
- MUSTThe syntax of the timestamp corresponds to the `msg-id' in [RFC822], and MUST be different each time the POP3 server issues a banner greeting.