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Internet Engineering Task Force (IETF)                           D. KarpRequest for Comments: 5957                                        ZimbraUpdates:5256                                                  July 2010Category: Standards TrackISSN: 2070-1721Display-Based Address Sorting for the IMAP4 SORT ExtensionAbstract   This document describes an IMAP protocol extension enabling server-   side message sorting on the commonly displayed portion of the From   and To header fields.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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc5957.Copyright Notice   Copyright (c) 2010 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Karp               IMAP4 Display-Based Address Sorting          [Page 1]

RFC 5957                                                       July 2010Table of Contents1. Introduction ....................................................22. Conventions Used in This Document ...............................23. DISPLAY Sort Value for an Address ...............................24. The DISPLAYFROM and DISPLAYTO Sort Criteria .....................35. Formal Syntax ...................................................36. Security Considerations .........................................37. Internationalization Considerations .............................48. IANA Considerations .............................................49. Normative References ............................................41.  Introduction   The [SORT] extension to the [IMAP] protocol provides a means for the   server-based sorting of messages.  It defines a set of sort criteria   and the mechanism for determining the sort value of a message for   each such ordering.   The [SORT] FROM and TO orderings sort messages lexically on the   [IMAP] addr-mailbox of the first address in the message's From and To   headers, respectively.  This document provides two alternative   orderings, DISPLAYFROM and DISPLAYTO, which sort messages based on   the first From or To address's [IMAP] addr-name (generally the same   as its [RFC5322] display-name), when present.   A server that supports the full [SORT] extension as well as both the   DISPLAYFROM and DISPLAYTO sort criteria indicates this by returning   "SORT=DISPLAY" in its CAPABILITY response.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 [RFC2119].3.  DISPLAY Sort Value for an Address   For the purposes of the sort criteria defined in this document, the   sort value for an [IMAP] address structure is defined as follows:   o  If the address structure's [IMAP] addr-name is non-NIL, apply the      procedure from[RFC5255], Section 4.6.  (That is, decode any      [RFC2047] encoded-words and convert the resulting character string      into a charset valid for the currently active [RFC4790] collation,      with a default of UTF-8.)  If the resulting octet string is not      the empty string, use it as the sort value for the address.Karp               IMAP4 Display-Based Address Sorting          [Page 2]

RFC 5957                                                       July 2010   o  Otherwise, if the address structure's [IMAP] addr-mailbox and      [IMAP] addr-host are both non-NIL, the sort value for the address      is addr-mailbox@addr-host.   o  Otherwise, if the address structure's [IMAP] addr-mailbox is non-      NIL, the sort value for the address is its addr-mailbox.   o  If none of the above conditions are met, the sort value for the      address is the empty string.4.  The DISPLAYFROM and DISPLAYTO Sort Criteria   This document introduces two new [SORT] sort criteria, DISPLAYFROM   and DISPLAYTO.  A message's sort value under these orderings MUST be   derived as follows:   A "derived-addr" value is created from the [IMAP] envelope structure   resulting from a FETCH ENVELOPE on the message.  For DISPLAYFROM, the   derived-addr value is the [IMAP] env-from value.  For DISPLAYTO, the   derived-addr value is the [IMAP] env-to value.   o  If the derived-addr value is NIL, the message's sort value is the      empty string.   o  Otherwise, the message's sort value is the DISPLAY sort value of      the first [IMAP] address in the derived-addr value.5.  Formal Syntax   The following syntax specification uses the Augmented Backus-Naur   Form (ABNF) notation as specified in [RFC5234].  [IMAP] defines the   non-terminal "capability", and [SORT] defines "sort-key".   capability    =/ "SORT=DISPLAY"   sort-key      =/ "DISPLAYFROM" / "DISPLAYTO"6.  Security Considerations   This document defines an additional IMAP4 capability.  As such, it   does not change the underlying security considerations of [IMAP].   The author believes that no new security issues are introduced with   this additional IMAP4 capability.Karp               IMAP4 Display-Based Address Sorting          [Page 3]

RFC 5957                                                       July 20107.  Internationalization Considerations   DISPLAYFROM and DISPLAYTO are string-based sort criteria.  As stated   in [SORT], the active [RFC4790] collation as per [RFC5255] MUST be   used when sorting such strings.   The DISPLAYFROM and DISPLAYTO orderings sort on the full decoded   [IMAP] addr-name, when present.  They do not attempt to parse this   string in a locale- or language-dependent manner in order to   determine and sort on some semantically meaningful substring such as   the surname.8.  IANA Considerations   [IMAP] capabilities are registered by publishing a Standards Track or   IESG-approved Experimental RFC.  This document constitutes   registration of the SORT=DISPLAY capability in the [IMAP]   capabilities registry.9.  Normative References   [IMAP]     Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION              4rev1",RFC 3501, March 2003.   [RFC2047]  Moore, K., "MIME (Multipurpose Internet Mail Extensions)              Part Three: Message Header Extensions for Non-ASCII Text",RFC 2047, November 1996.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC4790]  Newman, C., Duerst, M., and A. Gulbrandsen, "Internet              Application Protocol Collation Registry",RFC 4790, March              2007.   [RFC5234]  Crocker, D., Ed., and P. Overell, "Augmented BNF for              Syntax Specifications: ABNF", STD 68,RFC 5234, January              2008.   [RFC5255]  Newman, C., Gulbrandsen, A., and A. Melnikov, "Internet              Message Access Protocol Internationalization",RFC 5255,              June 2008.   [RFC5322]  Resnick, P., Ed., "Internet Message Format",RFC 5322,              October 2008.Karp               IMAP4 Display-Based Address Sorting          [Page 4]

RFC 5957                                                       July 2010   [SORT]     Crispin, M. and K. Murchison, "Internet Message Access              Protocol - SORT and THREAD Extensions",RFC 5256, June              2008.Author's Address   Dan Karp   Zimbra   3401 Hillview Avenue   Palo Alto, CA  94304   USA   EMail: dkarp@zimbra.com   URI:http://www.zimbra.comKarp               IMAP4 Display-Based Address Sorting          [Page 5]