
POP3 Extension Mechanism

The POP3 Extension Mechanism [RFC 2449] updates RFC 1939 to define a
mechanism to announce support for optional commands, extensions, and
unconditional server behavior.  Included is an initial set of
currently deployed capabilities which vary between server
implementations, and several new capabilities (SASL, RESP-CODES,
LOGIN-DELAY, PIPELINING, EXPIRE and IMPLEMENTATION).  The RFC also
extends POP3 error messages so that machine parsable codes can be
provided to the client.


POP3 capabilities

New POP3 capabilities MUST be defined in a standards track or IESG
approved experimental RFC, and MUST NOT begin with the letter "X".

New POP3 capabilities MUST include the following information:

	CAPA tag
	Arguments
	Added commands
	Standard commands affected
	Announced states / possible differences
	Commands valid in states
	Specification reference
	Discussion


Initial Set of Capabilities

	TOP						[RFC2449]
	USER						[RFC2449]
	SASL						[RFC2449]
	RESP-CODES					[RFC2449]
	LOGIN-DELAY					[RFC2449]
	PIPELINING					[RFC2449]
	EXPIRE						[RFC2449]
	UIDL						[RFC2449]
	IMPLEMENTATION					[RFC2449]


POP3 Response Codes

New POP3 response codes MUST be defined in an RFC or other permanent
and readily available reference, in sufficient detail so that
interoperability between independent implementations is possible.

New POP3 response code specifications MUST include the following
information: the complete response code, for which responses (+OK or
-ERR) and commands it is valid, and a definition of its meaning and
expectedNew POP3 response codes MUST be defined in an RFC or other
permanent and readily available reference, in sufficient detail so
that interoperability between independent implementations is possible.

New POP3 response code specifications MUST include the following
information: the complete response code, for which responses (+OK or
-ERR) and commands it is valid, and a definition of its meaning and
expected client behavior. client behavior.


Initial POP3 response codes

	LOGIN-DELAY					[RFC2449]
	IN-USE                                          [RFC2449]




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



