Post Office Protocol version 3 (POP3) Extension Mechanism

Last Updated
2013-03-13
Note
The POP3 Extension Mechanism [RFC 2449] updates [RFC 1939] to define a
mechanism to announce support for optional commands, extensions, and
unconditional server behavior.  Please see Section 1 of [RFC 2449]  for
details regarding POP3 Extensions.
Available Formats

XML
HTML
TXT

Registries Included Below

POP3 Capabilities

Registration Procedure(s)
Standards Track or IESG-approved Experimental RFC
Reference
[RFC 2449]
Available Formats

CSV
CAPA Tag CAPA Args Added Cmds Cmds Affected List Diffs Cmd Valid References
TOP none TOP none both no TRANSACTION [RFC 2449][RFC 1939]
USER none USER, PASS none both no AUTHENTICATION [RFC 2449][RFC 1939]
SASL mech list AUTH none both no AUTHENTICATION [RFC 2449][RFC 5034]
RESP-CODES none none none both no n/a [RFC 2449]
LOGIN-DELAY secs, USER none USER, PASS, APOP, AUTH both yes n/a [RFC 2449]
PIPELINING none none all both no n/a [RFC 2449]
EXPIRE days, NEVER, USER none none both yes n/a [RFC 2449]
UIDL none UIDL none both no TRANSACTION [RFC 2449][RFC 1939]
IMPLEMENTATION text none none TRANS, both no n/a [RFC 2449][RFC 1939]
STLS none STLS USER, PASS, CAPA both no AUTHENTICATION [RFC 2595]
AUTH-RESP-CODE none none none both no n/a [RFC 3206]
UTF8 USER UTF8 USER, PASS, APOP, LIST, TOP, RETR both no AUTHORIZATION [RFC 6856]
LANG none LANG all both no AUTHORIZATION TRANSACTION [RFC 6856]

POP3 Response Codes

Registration Procedure(s)
RFC Specification Required
Reference
[RFC 2449]
Note
See Section 9 of [RFC 2449] for details regarding Response Codes.
Available Formats

CSV
Response Code Response Types Commands Reference
LOGIN-DELAY -ERR USER[1], PASS, APOP, AUTH [RFC 2449]
IN-USE -ERR PASS, APOP, AUTH [RFC 2449]
SYS/PERM -ERR All commands [RFC 3206]
SYS/TEMP -ERR All commands [RFC 3206]
AUTH -ERR Any authentication command including AUTH USER [2], PASS, or APOP. [RFC 3206]
UTF8 -ERR LIST, TOP, RETR [RFC 6856]

Footnotes

[1] 
see spec for details
[2] 
Returning the AUTH response code to the USER command reveals
to the client that the specified user exists.  It is strongly
RECOMMENDED that the server not issue this response code to the
USER command.