Post Office Protocol version 3 (POP3) Extension Mechanism
2013-03-13
The POP3 Extension Mechanism updates to define a
mechanism to announce support for optional commands, extensions, and
unconditional server behavior. Please see Section 1 of for
details regarding POP3 Extensions.
POP3 Capabilities
Standards Track or IESG-approved Experimental RFC
TOP
none
TOP
none
both
no
TRANSACTION
USER
none
USER,
PASS
none
both
no
AUTHENTICATION
SASL
mech list
AUTH
none
both
no
AUTHENTICATION
RESP-CODES
none
none
none
both
no
n/a
LOGIN-DELAY
secs,
USER
none
USER,
PASS,
APOP,
AUTH
both
yes
n/a
PIPELINING
none
none
all
both
no
n/a
EXPIRE
days,
NEVER,
USER
none
none
both
yes
n/a
UIDL
none
UIDL
none
both
no
TRANSACTION
IMPLEMENTATION
text
none
none
TRANS,
both
no
n/a
STLS
none
STLS
USER,
PASS,
CAPA
both
no
AUTHENTICATION
AUTH-RESP-CODE
none
none
none
both
no
n/a
UTF8
USER
UTF8
USER,
PASS,
APOP,
LIST,
TOP,
RETR
both
no
AUTHORIZATION
LANG
none
LANG
all
both
no
AUTHORIZATION
TRANSACTION
POP3 Response Codes
RFC Specification Required
See Section 9 of for details regarding Response Codes.
LOGIN-DELAY
-ERR
USER, PASS, APOP, AUTH
IN-USE
-ERR
PASS, APOP, AUTH
SYS/PERM
-ERR
All commands
SYS/TEMP
-ERR
All commands
AUTH
-ERR
Any authentication command
including AUTH USER ,
PASS, or APOP.
UTF8
-ERR
LIST, TOP, RETR
see spec for details
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.