Post Office Protocol version 3 (POP3) Extension Mechanism

Last Updated
2013-03-13
Note
The POP3 Extension Mechanism [RFC2449] updates [RFC1939] to define a
mechanism to announce support for optional commands, extensions, and
unconditional server behavior.  Please see Section 1 of [RFC2449]  for
details regarding POP3 Extensions.
Available Formats

XML
HTML
Plain text

Registries included below

POP3 Capabilities

Registration Procedure(s)
Standards Track or IESG-approved Experimental RFC
Reference
[RFC2449]
Available Formats

CSV
CAPA Tag CAPA Args Added Cmds Cmds Affected List Diffs Cmd Valid References
TOP none TOP none both no TRANSACTION [RFC2449][RFC1939]
USER none USER, PASS none both no AUTHENTICATION [RFC2449][RFC1939]
SASL mech list AUTH none both no AUTHENTICATION [RFC2449][RFC5034]
RESP-CODES none none none both no n/a [RFC2449]
LOGIN-DELAY secs, USER none USER, PASS, APOP, AUTH both yes n/a [RFC2449]
PIPELINING none none all both no n/a [RFC2449]
EXPIRE days, NEVER, USER none none both yes n/a [RFC2449]
UIDL none UIDL none both no TRANSACTION [RFC2449][RFC1939]
IMPLEMENTATION text none none TRANS, both no n/a [RFC2449][RFC1939]
STLS none STLS USER, PASS, CAPA both no AUTHENTICATION [RFC2595]
AUTH-RESP-CODE none none none both no n/a [RFC3206]
UTF8 USER UTF8 USER, PASS, APOP, LIST, TOP, RETR both no AUTHORIZATION [RFC6856]
LANG none LANG all both no AUTHORIZATION TRANSACTION [RFC6856]

POP3 Response Codes

Registration Procedure(s)
RFC Specification Required
Reference
[RFC2449]
Note
See Section 9 of [RFC2449] for details regarding Response Codes.
Available Formats

CSV
Response Code Response Types Commands Reference
LOGIN-DELAY -ERR USER[1], PASS, APOP, AUTH [RFC2449]
IN-USE -ERR PASS, APOP, AUTH [RFC2449]
SYS/PERM -ERR All commands [RFC3206]
SYS/TEMP -ERR All commands [RFC3206]
AUTH -ERR Any authentication command including AUTH USER [2], PASS, or APOP. [RFC3206]
UTF8 -ERR LIST, TOP, RETR [RFC6856]

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.