Post Office Protocol version 3 (POP3) Extension Mechanism

(last updated 2012-05-21)

Registries included below:
- POP3 Capabilities
- POP3 Response Codes

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.


Registry Name: POP3 Capabilities
Reference: [RFC2449]
Registration Procedures: Standards Track or IESG approved experimental RFC

Registry:
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,       none           both         no         AUTHENTICATION  [RFC2449][RFC1939]
                            PASS

SASL            mech list   AUTH        none           both         no         AUTHENTICATION  [RFC2449][RFC5034]

RESP-CODES      none        none        none           both         no         n/a             [RFC2449]

LOGIN-DELAY     secs,       none        USER,          both         yes        n/a             [RFC2449]
                USER                    PASS, 
                                        APOP, 
                                        AUTH

PIPELINING      none        none        all            both         no         n/a             [RFC2449]

EXPIRE          days,       none        none           both         yes        n/a             [RFC2449]
                NEVER, 
                USER

UIDL            none        UIDL        none           both         no         TRANSACTION     [RFC2449][RFC1939]

IMPLEMENTATION  text        none        none           TRANS,       no         n/a             [RFC2449][RFC1939]
                                                       both

STLS            none        STLS        USER,          both         no         AUTHENTICATION  [RFC2595]
                                        PASS, 
                                        CAPA

AUTH-RESP-CODE  none        none        none           both         no         n/a             [RFC3206]

UTF8            USER        UTF8        USER,          both         no         AUTHORIZATION   [RFC5721]
                                        PASS,
                                        APOP, 
                                        LIST, 
                                        TOP, 
                                        RETR

LANG            none        LANG        all            both         no         AUTHORIZATION   [RFC5721]
                                                                               TRANSACTION


Registry Name: POP3 Response Codes
Reference: [RFC2449]
Registration Procedures: RFC Specification Required

Note: Please see section 9 of RFC2449 for details regarding Response Codes.

* - see spec for details

Note: 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.

Registry:
Response Code  Response Types  Commands                           Reference
-------------  --------------  ---------------------------------  ---------
LOGIN-DELAY    -ERR            USER*, 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         [RFC3206]
                               including AUTH USER (see note),
                               PASS, or APOP.


References
----------
[RFC1734] Myers, J., "POP3 AUTHentication command", RFC 1734, December
          1994.

[RFC1939] Myers, J. and M. Rose, "Post Office Protocol -- Version 3",
          STD 53, RFC 1939, May 1996.

[RFC2449] Gellens, R., Newman, C. and L. Lundblade, "POP3 Extension
          Mechanism", RFC 2449, November 1998.

[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595,
          Innosoft, June 1999.

[RFC3206] R. Gellens, "The SYS and AUTH POP Response Codes", RFC3206,
          February 2002.

[RFC5034] R. Siemborski, A. Menon-Sen, "POP3 SASL Authentication 
          Mechanism",  RFC 5034, July 2007.

[RFC5721] R. Gellens, C. Newman, "POP3 Support for UTF-8", RFC 5721,
          February 2010.

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