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RFC 5788 - IMAP4 Keyword Registry


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Internet Engineering Task Force (IETF)                       A. Melnikov
Request for Comments: 5788                                   D. Cridland
Category: Standards Track                                  Isode Limited
ISSN: 2070-1721                                               March 2010

                         IMAP4 Keyword Registry

Abstract

   The aim of this document is to establish a new IANA registry for IMAP
   keywords and to define a procedure for keyword registration, in order
   to improve interoperability between different IMAP clients.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5788.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................2
   2. Conventions Used in This Document ...............................2
   3. IANA Considerations .............................................3
      3.1. Review Guidelines for the Designated Expert Reviewer .......4
      3.2. Comments on IMAP Keywords' Registrations ...................5
      3.3. Change Control .............................................5
      3.4. Initial Registrations ......................................6
           3.4.1. $MDNSent IMAP Keyword Registration ..................6
           3.4.2. $Forwarded IMAP Keyword Registration ................7
           3.4.3. $SubmitPending IMAP Keyword Registration ............8
           3.4.4. $Submitted IMAP Keyword Registration ................9
   4. Security Considerations ........................................10
   5. Acknowledgements ...............................................10
   6. References .....................................................10
      6.1. Normative References ......................................10
      6.2. Informative References ....................................11

1.  Introduction

   IMAP keywords [RFC3501] are boolean named flags that can be used by
   clients to annotate messages in an IMAP mailbox.  Although IMAP
   keywords are an optional feature of IMAP, the majority of IMAP
   servers can store arbitrary keywords.  Many mainstream IMAP clients
   use a limited set of specific keywords, and some can manage (create,
   edit, display) arbitrary IMAP keywords.

   Over the years, some IMAP keywords have become de-facto standards,
   with some specific semantics associated with them.  In some cases,
   different client implementors decided to define and use keywords with
   different names, but the same semantics.  Some server implementors
   decided to map such keywords automatically in order to improve cross-
   client interoperability.

   In other cases, the same keywords have been used with different
   semantics, thus causing interoperability problems.

   This document attempts to prevent further incompatible uses of IMAP
   keywords by establishing an "IMAP Keywords" registry and allocating a
   special prefix for standardized keywords.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [Kwds].

3.  IANA Considerations

   IANA has established a new registry for IMAP keywords.

   Registration of an IMAP keyword is requested by filling in the
   following template and following the instructions on the IANA pages
   for the registry to submit it to IANA:

   Subject:    Registration of IMAP keyword X

   IMAP keyword name:

   Purpose (description):

   Private or Shared on a server:  (One of PRIVATE, SHARED, or BOTH.
                                   PRIVATE means that each different
                                   user has a distinct copy of the
                                   keyword.  SHARED means that all
                                   different users see the same value of
                                   the keyword.  BOTH means that an IMAP
                                   server can have the keyword as either
                                   private or shared.)

   Is it an advisory keyword or may it cause an automatic action:

   When/by whom the keyword is set/cleared:

   Related keywords:  (for example, "mutually exclusive with keywords Y
                      and Z")

   Related IMAP capabilities:

   Security considerations:

   Published specification (recommended):

   Person & email address to contact for further information:

   Intended usage:  (One of COMMON, LIMITED USE, or DEPRECATED (i.e.,
                    not recommended for use))

   Owner/Change controller:  (MUST be "IESG" for any "common use"
                             keyword registration specified in an IETF
                             Review document.  See definition of "common
                             use" below in this section.  When the
                             Owner/Change controller is not a
                             Standardization Organization, the
                             registration request MUST make it clear if

                             the registration is controlled by a
                             company, or the individual performing the
                             registration.)

   Note:       (Any other information that the author deems interesting
               may be added here, for example, if the keyword(s) is
               supported by existing clients.)

   Registration of an IMAP keyword requires Expert Review [RFC5226].
   Registration of any IMAP keyword is initiated by posting a
   registration request to the Message Organization WG mailing list
   <morg@ietf.org> (or its replacement as chosen by the responsible
   Application Area Director) and CCing IANA (<iana@iana.org>).  After
   allowing for at least two weeks for community input on the designated
   mailing list, the expert will determine the appropriateness of the
   registration request and either approve or disapprove the request
   with notice to the requestor, the mailing list, and IANA.  Any
   refusal must come with a clear explanation.

   The IESG appoints one or more Expert Reviewers for the IMAP keyword
   registry established by this document.

   The Expert Reviewer should strive for timely reviews.  The Expert
   Reviewer should take no longer than six weeks to make and announce
   the decision, or notify the mailing list that more time is required.

   Decisions (or lack of) made by an Expert Reviewer can be first
   appealed to Application Area Directors and, if the appellant is not
   satisfied with the response, to the full IESG.

   There are two types of IMAP keywords in the "IMAP Keywords" registry:
   intended for "common use" and vendor-/organization-specific use (also
   known as "limited use").  An IMAP keyword is said to be for "common
   use" if it is reasonably expected to be implemented in at least two
   independent client implementations.  The two types of IMAP keywords
   have different levels of requirements for registration (see below).

3.1.  Review Guidelines for the Designated Expert Reviewer

   Expert Reviewers should focus on the following requirements.

   Registration of a vendor-/organization-specific ("limited use") IMAP
   keyword is easier.  The Expert Reviewer only needs to check that the
   requested name doesn't conflict with an already registered name, and
   that the name is not too generic, misleading, etc.  The Expert
   Reviewer MAY request the IMAP keyword name change before approving

   the registration.  The Expert Reviewer SHOULD refuse a registration
   if there is an already registered IMAP keyword that serves the same
   purpose, but has a different name.

   When registering an IMAP keyword for "common use", the Expert
   Reviewer performs the checks described for vendor-/
   organization-specific IMAP keywords, plus additional checks as
   detailed below.

   Keywords intended for "common use" SHOULD start with the "$" prefix.
   (Note that this is a SHOULD because some of the commonly used IMAP
   keywords in widespread use don't follow this convention.)

   IMAP keywords intended for "common use" SHOULD be standardized in
   IETF Review [RFC5226] documents.  (Note that IETF Review documents
   still require Expert Review.)

   Values in the "IMAP Keywords" IANA registry intended for "common use"
   must be clearly documented and likely to ensure interoperability.
   They must be useful, not harmful to the Internet.  In cases when an
   IMAP keyword being registered is already deployed, Expert Reviewers
   should favor registering it over requiring perfect documentation
   and/or requesting a change to the name of the IMAP keyword.

   The Expert Reviewer MAY automatically "upgrade" registration requests
   for a "limited use" IMAP keyword to "common use" level.  The Expert
   Reviewer MAY also request that a registration targeted for "common
   use" be registered as "limited use" instead.

3.2.  Comments on IMAP Keywords' Registrations

   Comments on registered IMAP keywords should be sent to both the
   "owner" of the mechanism and to the mailing list designated to IMAP
   keyword review (see Section 3).  This improves the chances of getting
   a timely response.

   Submitters of comments may, after a reasonable attempt to contact the
   owner and after soliciting comments on the IMAP mailing list, request
   the designated Expert Reviewer to attach their comment to the IMAP
   keyword registration itself.  The procedure is similar to requesting
   an Expert Review for the affected keyword.

3.3.  Change Control

   Once an IMAP keyword registration has been published by IANA, the
   owner may request a change to its definition.  The change request
   (including a change to the "intended usage" field) follows the same
   procedure as the initial registration request, with the exception of

   changes to the "Person & email address to contact for further
   information" and "Owner/Change controller" fields.  The latter can be
   changed by the owner by informing IANA; this can be done without
   discussion or review.

   The IESG may reassign responsibility for an IMAP keyword.  The most
   common case of this will be to enable clarifications to be made to
   keywords where the owner of the registration has died, moved out of
   contact, or is otherwise unable to make changes that are important to
   the community.

   IMAP keyword registrations MUST NOT be deleted; keywords that are no
   longer believed appropriate for use can be declared DEPRECATED by a
   change to their "intended usage" field.

   The IESG is considered the owner of all "common use" IMAP keywords
   that are published in an IETF Review document.

3.4.  Initial Registrations

   IANA has registered the IMAP keywords specified in following
   subsections in the registry established by this document.

3.4.1.  $MDNSent IMAP Keyword Registration

   Subject:    Registration of IMAP keyword $MDNSent

   IMAP keyword name:  $MDNSent

   Purpose (description):  Specifies that a Message Disposition
                           Notification (MDN) must not be sent for any
                           message annotated with the $MDNSent IMAP
                           keyword.

   Private or Shared on a server:  SHARED

   Is it an advisory keyword or may it cause an automatic action:
                           This keyword can cause automatic action by
                           the client.  See [RFC3503] for more details.

   When/by whom the keyword is set/cleared:
                           This keyword is set by an IMAP client when it
                           decides to act on an MDN request, or when
                           uploading a sent or draft message.  It can
                           also be set by a delivery agent.  Once set,
                           the flag SHOULD NOT be cleared.

   Related keywords:  None

   Related IMAP capabilities:  None

   Security considerations:  See Section 6 of [RFC3503]

   Published specification (recommended):  [RFC3503]

   Person & email address to contact for further information:
                           Alexey Melnikov <alexey.melnikov@isode.com>

   Intended usage:  COMMON

   Owner/Change controller:  IESG

   Note:

3.4.2.  $Forwarded IMAP Keyword Registration

   Subject:    Registration of the IMAP keyword $Forwarded

   IMAP keyword name:  $Forwarded

   Purpose (description):  $Forwarded is used by several IMAP clients to
                           specify that the message was resent to
                           another email address, embedded within or
                           attached to a new message.  This keyword is
                           set by the mail client when it successfully
                           forwards the message to another email
                           address.  Typical usage of this keyword is to
                           show a different (or additional) icon for a
                           message that has been forwarded.

   Private or Shared on a server:  BOTH

   Is it an advisory keyword or may it cause an automatic action:
                           advisory

   When/by whom the keyword is set/cleared:
                           This keyword can be set by either a delivery
                           agent or a mail client.  Once set, the flag
                           SHOULD NOT be cleared.  Notes: There is no
                           way to tell if a message with $Forwarded
                           keyword set was forwarded more than once.

   Related keywords:  None

   Related IMAP capabilities:  None

   Security considerations:  A server implementing this keyword as a
                             shared keyword may disclose that a
                             confidential message was forwarded.

   Published specification (recommended):  [RFC5550]

   Person & email address to contact for further information:
                           Alexey Melnikov <alexey.melnikov@isode.com>

   Intended usage:  COMMON

   Owner/Change controller:  IESG

   Note:

3.4.3.  $SubmitPending IMAP Keyword Registration

   Subject:    Registration of IMAP keyword $SubmitPending

   IMAP keyword name:  $SubmitPending

   Purpose (description):  The $SubmitPending IMAP keyword designates
                           the message as awaiting to be submitted.
                           This keyword allows storing messages waiting
                           to be submitted in the same mailbox where
                           messages that were already submitted and/or
                           are being edited are stored.

                           A message that has both $Submitted and
                           $SubmitPending IMAP keywords set is a message
                           being actively submitted.

   Private or Shared on a server:  SHARED

   Is it an advisory keyword or may it cause an automatic action:
                            This keyword can cause automatic action by
                           the client.  See Section 5.10 of [RFC5550]
                           for more details.

   When/by whom the keyword is set/cleared:
                           This keyword is set by a mail client when it
                           decides that the message needs to be sent
                           out.

   Related keywords:  $Submitted

   Related IMAP capabilities:  None

   Security considerations:  A server implementing this keyword as a
                             shared keyword may disclose that a
                             confidential message is scheduled to be
                             sent out or is being actively sent out.

   Published specification (recommended):  [RFC5550]

   Person & email address to contact for further information:
                           Alexey Melnikov <alexey.melnikov@isode.com>

   Intended usage:  COMMON

   Owner/Change controller:  IESG

   Note:

3.4.4.  $Submitted IMAP Keyword Registration

   Subject:    Registration of IMAP keyword $Submitted

   IMAP keyword name:  $Submitted

   Purpose (description):  The $Submitted IMAP keyword designates the
                           message as being sent out.

                           A message that has both $Submitted and
                           $SubmitPending IMAP keywords set is a message
                           being actively submitted.

   Private or Shared on a server:  SHARED

   Is it an advisory keyword or may it cause an automatic action:
                           This keyword can cause automatic action by
                           the client.  See Section 5.10 of [RFC5550]
                           for more details.

   When/by whom the keyword is set/cleared:
                           This keyword is set by a mail client when it
                           decides to start sending it.

   Related keywords:  $SubmitPending

   Related IMAP capabilities:  None

   Security considerations:  A server implementing this keyword as a
                             shared keyword may disclose that a
                             confidential message was sent or is being
                             actively sent out.

   Published specification (recommended):  [RFC5550]

   Person & email address to contact for further information:
                           Alexey Melnikov <alexey.melnikov@isode.com>

   Intended usage:  COMMON

   Owner/Change controller:  IESG

   Note:

4.  Security Considerations

    IMAP keywords are one of the base IMAP features [RFC3501].  This
    document doesn't change their behavior, so it does not add new
    security issues.

    A particular IMAP keyword might have specific security
    considerations, which are documented in the IMAP keyword
    registration template standardized by this document.

5.  Acknowledgements

   The creation of this document was prompted by one of many discussions
   on the IMAP mailing list.

   John Neystadt co-authored the first version of this document.

   Special thanks to Chris Newman, David Harris, Lyndon Nerenberg, Mark
   Crispin, Samuel Weiler, Alfred Hoenes, Lars Eggert, and Cullen
   Jennings for reviewing different versions of this document.  However,
   all errors or omissions must be attributed to the authors of this
   document.

   The authors would also like to thank the developers of Mozilla mail
   clients for providing food for thought.

6.  References

6.1.  Normative References

   [Kwds]     Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, March 2003.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

6.2.  Informative References

   [RFC3503]  Melnikov, A., "Message Disposition Notification (MDN)
              profile for Internet Message Access Protocol (IMAP)",
              RFC 3503, March 2003.

   [RFC5550]  Cridland, D., Melnikov, A., and S. Maes, "The Internet
              Email to Support Diverse Service Environments (Lemonade)
              Profile", RFC 5550, August 2009.

Authors' Addresses

   Alexey Melnikov
   Isode Limited
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   EMail: Alexey.Melnikov@isode.com
   URI:   http://www.melnikov.ca/

   Dave Cridland
   Isode Limited
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   EMail: dave.cridland@isode.com

 

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