RFC5530
Network Working Group A. Gulbrandsen Request for Comments: 5530 Oryx Mail Systems GmbH Category: Standards Track May 2009
IMAP Response Codes
Status of This Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
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Abstract
IMAP responses consist of a response type (OK, NO, BAD), an optional machine-readable response code, and a human-readable text.
This document collects and documents a variety of machine-readable response codes, for better interoperation and error reporting.
Contents
Introduction
Section 7.1 of RFC3501 defines a number of response codes that can help tell an IMAP client why a command failed. However, experience has shown that more codes are useful. For example, it is useful for a client to know that an authentication attempt failed because of a server problem as opposed to a password problem.
Currently, many IMAP servers use English-language, human-readable text to describe these errors, and a few IMAP clients attempt to translate this text into the user's language.
This document names a variety of errors as response codes. It is based on errors that have been checked and reported on in some IMAP server implementations, and on the needs of some IMAP clients.
This document doesn't require any servers to test for these errors or any clients to test for these names. It only names errors for better reporting and handling.
Conventions Used in This Document
Formal syntax is defined by RFC5234 as modified by RFC3501.
Example lines prefaced by "C:" are sent by the client and ones prefaced by "S:" by the server. "[...]" means elision.
Response Codes
This section defines all the new response codes. Each definition is followed by one or more examples.
UNAVAILABLE
Temporary failure because a subsystem is down. For example, an
IMAP server that uses a Lightweight Directory Access Protocol
(LDAP) or Radius server for authentication might use this
response code when the LDAP/Radius server is down.
C: a LOGIN "fred" "foo"
S: a NO [UNAVAILABLE] User's backend down for maintenance
AUTHENTICATIONFAILED
Authentication failed for some reason on which the server is
unwilling to elaborate. Typically, this includes "unknown
user" and "bad password".
This is the same as not sending any response code, except that
when a client sees AUTHENTICATIONFAILED, it knows that the
problem wasn't, e.g., UNAVAILABLE, so there's no point in
trying the same login/password again later.
C: b LOGIN "fred" "foo"
S: b NO [AUTHENTICATIONFAILED] Authentication failed
AUTHORIZATIONFAILED
Authentication succeeded in using the authentication identity,
but the server cannot or will not allow the authentication
identity to act as the requested authorization identity. This
is only applicable when the authentication and authorization
identities are different.
C: c1 AUTHENTICATE PLAIN
[...]
S: c1 NO [AUTHORIZATIONFAILED] No such authorization-ID
C: c2 AUTHENTICATE PLAIN
[...]
S: c2 NO [AUTHORIZATIONFAILED] Authenticator is not an admin
EXPIRED
Either authentication succeeded or the server no longer had the
necessary data; either way, access is no longer permitted using
that passphrase. The client or user should get a new
passphrase.
C: d login "fred" "foo"
S: d NO [EXPIRED] That password isn't valid any more
PRIVACYREQUIRED
The operation is not permitted due to a lack of privacy. If
Transport Layer Security (TLS) is not in use, the client could
try STARTTLS (see Section 6.2.1 of RFC3501) and then repeat
the operation.
C: d login "fred" "foo"
S: d NO [PRIVACYREQUIRED] Connection offers no privacy
C: d select inbox
S: d NO [PRIVACYREQUIRED] Connection offers no privacy
CONTACTADMIN
The user should contact the system administrator or support
desk.
C: e login "fred" "foo"
S: e OK [CONTACTADMIN]
NOPERM
The access control system (e.g., Access Control List (ACL), see
RFC4314) does not permit this user to carry out an operation,
such as selecting or creating a mailbox.
C: f select "/archive/projects/experiment-iv"
S: f NO [NOPERM] Access denied
INUSE
An operation has not been carried out because it involves
sawing off a branch someone else is sitting on. Someone else
may be holding an exclusive lock needed for this operation, or
the operation may involve deleting a resource someone else is
using, typically a mailbox.
The operation may succeed if the client tries again later.
C: g delete "/archive/projects/experiment-iv"
S: g NO [INUSE] Mailbox in use
EXPUNGEISSUED
Someone else has issued an EXPUNGE for the same mailbox. The
client may want to issue NOOP soon. RFC2180 discusses this
subject in depth.
C: h search from [email protected] S: * SEARCH 1 2 3 5 8 13 21 42 S: h OK [EXPUNGEISSUED] Search completed
CORRUPTION
The server discovered that some relevant data (e.g., the
mailbox) are corrupt. This response code does not include any
information about what's corrupt, but the server can write that
to its logfiles.
C: i select "/archive/projects/experiment-iv"
S: i NO [CORRUPTION] Cannot open mailbox
SERVERBUG
The server encountered a bug in itself or violated one of its
own invariants.
C: j select "/archive/projects/experiment-iv"
S: j NO [SERVERBUG] This should not happen
CLIENTBUG
The server has detected a client bug. This can accompany all
of OK, NO, and BAD, depending on what the client bug is.
C: k1 select "/archive/projects/experiment-iv"
[...]
S: k1 OK [READ-ONLY] Done
C: k2 status "/archive/projects/experiment-iv" (messages)
[...]
S: k2 OK [CLIENTBUG] Done
CANNOT
The operation violates some invariant of the server and can
never succeed.
C: l create "///////"
S: l NO [CANNOT] Adjacent slashes are not supported
LIMIT
The operation ran up against an implementation limit of some
kind, such as the number of flags on a single message or the
number of flags used in a mailbox.
C: m STORE 42 FLAGS f1 f2 f3 f4 f5 ... f250
S: m NO [LIMIT] At most 32 flags in one mailbox supported
OVERQUOTA
The user would be over quota after the operation. (The user
may or may not be over quota already.)
Note that if the server sends OVERQUOTA but doesn't support the
IMAP QUOTA extension defined by RFC2087, then there is a
quota, but the client cannot find out what the quota is.
C: n1 uid copy 1:* oldmail
S: n1 NO [OVERQUOTA] Sorry
C: n2 uid copy 1:* oldmail
S: n2 OK [OVERQUOTA] You are now over your soft quota
ALREADYEXISTS
The operation attempts to create something that already exists,
such as when the CREATE or RENAME directories attempt to create
a mailbox and there is already one of that name.
C: o RENAME this that
S: o NO [ALREADYEXISTS] Mailbox "that" already exists
NONEXISTENT
The operation attempts to delete something that does not exist.
Similar to ALREADYEXISTS.
C: p RENAME this that
S: p NO [NONEXISTENT] No such mailbox
Formal Syntax
The following syntax specification uses the Augmented Backus-Naur Form (ABNF) notation as specified in RFC5234. RFC3501 defines the non-terminal "resp-text-code".
Except as noted otherwise, all alphabetic characters are case- insensitive. The use of upper or lowercase characters to define token strings is for editorial clarity only.
resp-text-code =/ "UNAVAILABLE" / "AUTHENTICATIONFAILED" /
"AUTHORIZATIONFAILED" / "EXPIRED" /
"PRIVACYREQUIRED" / "CONTACTADMIN" / "NOPERM" /
"INUSE" / "EXPUNGEISSUED" / "CORRUPTION" /
"SERVERBUG" / "CLIENTBUG" / "CANNOT" /
"LIMIT" / "OVERQUOTA" / "ALREADYEXISTS" /
"NONEXISTENT"
Security Considerations
Revealing information about a passphrase to unauthenticated IMAP clients causes bad karma.
Response codes are easier to parse than human-readable text. This can amplify the consequences of an information leak. For example, selecting a mailbox can fail because the mailbox doesn't exist, because the user doesn't have the "l" right (right to know the mailbox exists) or "r" right (right to read the mailbox). If the server sent different responses in the first two cases in the past, only malevolent clients would discover it. With response codes it's possible, perhaps probable, that benevolent clients will forward the
leaked information to the user. Server authors are encouraged to be particularly careful with the NOPERM and authentication-related responses.
IANA Considerations
The IANA has created the IMAP Response Codes registry. The registry has been populated with the following codes:
NEWNAME RFC 2060 (obsolete) REFERRAL RFC 2221 ALERT RFC 3501 BADCHARSET RFC 3501 PARSE RFC 3501 PERMANENTFLAGS RFC 3501 READ-ONLY RFC 3501 READ-WRITE RFC 3501 TRYCREATE RFC 3501 UIDNEXT RFC 3501 UIDVALIDITY RFC 3501 UNSEEN RFC 3501 UNKNOWN-CTE RFC 3516 UIDNOTSTICKY RFC 4315 APPENDUID RFC 4315 COPYUID RFC 4315 URLMECH RFC 4467 TOOBIG RFC 4469 BADURL RFC 4469 HIGHESTMODSEQ RFC 4551 NOMODSEQ RFC 4551 MODIFIED RFC 4551 COMPRESSIONACTIVE RFC 4978 CLOSED RFC 5162 NOTSAVED RFC 5182 BADCOMPARATOR RFC 5255 ANNOTATE RFC 5257 ANNOTATIONS RFC 5257 TEMPFAIL RFC 5259 MAXCONVERTMESSAGES RFC 5259 MAXCONVERTPARTS RFC 5259 NOUPDATE RFC 5267 METADATA RFC 5464 NOTIFICATIONOVERFLOW RFC 5465 BADEVENT RFC 5465 UNDEFINED-FILTER RFC 5466 UNAVAILABLE RFC 5530 AUTHENTICATIONFAILED RFC 5530 AUTHORIZATIONFAILED RFC 5530
EXPIRED RFC 5530 PRIVACYREQUIRED RFC 5530 CONTACTADMIN RFC 5530 NOPERM RFC 5530 INUSE RFC 5530 EXPUNGEISSUED RFC 5530 CORRUPTION RFC 5530 SERVERBUG RFC 5530 CLIENTBUG RFC 5530 CANNOT RFC 5530 LIMIT RFC 5530 OVERQUOTA RFC 5530 ALREADYEXISTS RFC 5530 NONEXISTENT RFC 5530
The new registry can be extended by sending a registration request to IANA. IANA will forward this request to a Designated Expert, appointed by the responsible IESG Area Director, CCing it to the IMAP Extensions mailing list at <[email protected]> (or a successor designated by the Area Director). After either allowing 30 days for community input on the IMAP Extensions mailing list or a successful IETF Last Call, the expert will determine the appropriateness of the registration request and either approve or disapprove the request by sending a notice of the decision to the requestor, CCing the IMAP Extensions mailing list and IANA. A denial notice must be justified by an explanation, and, in cases where it is possible, concrete suggestions on how the request can be modified so as to become acceptable should be provided.
For each response code, the registry contains a list of relevant RFCs that describe (or extend) the response code and an optional response code status description, such as "obsolete" or "reserved to prevent collision with deployed software". (Note that in the latter case, the RFC number can be missing.) Presence of the response code status description means that the corresponding response code is NOT RECOMMENDED for widespread use.
The intention is that any future allocation will be accompanied by a published RFC (including direct submissions to the RFC Editor). But in order to allow for the allocation of values prior to the RFC being approved for publication, the Designated Expert can approve allocations once it seems clear that an RFC will be published, for example, before requesting IETF LC for the document.
The Designated Expert can also approve registrations for response codes used in deployed software when no RFC exists. Such registrations must be marked as "reserved to prevent collision with deployed software".
Response code registrations may not be deleted; response codes that are no longer believed appropriate for use (for example, if there is a problem with the syntax of said response code or if the specification describing it was moved to Historic) should be marked "obsolete" in the registry, clearly marking the lists published by IANA.
Acknowledgements
Peter Coates, Mark Crispin, Philip Guenther, Alexey Melnikov, Ken Murchison, Chris Newman, Timo Sirainen, Philip Van Hoof, Dale Wiggins, and Sarah Wilkin helped with this document.
References
Normative References
RFC3501 Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
RFC5234 Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008.
Informative References
RFC2087 Myers, J., "IMAP4 QUOTA extension", RFC 2087, January
1997.
RFC2180 Gahrns, M., "IMAP4 Multi-Accessed Mailbox Practice", RFC
2180, July 1997.
RFC4314 Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
RFC 4314, December 2005.
Author's Address
Arnt Gulbrandsen Oryx Mail Systems GmbH Schweppermannstr. 8 D-81671 Muenchen Germany
Fax: +49 89 4502 9758 EMail: [email protected]
