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rfc:rfc5957

Internet Engineering Task Force (IETF) D. Karp Request for Comments: 5957 Zimbra Updates: 5256 July 2010 Category: Standards Track ISSN: 2070-1721

     Display-Based Address Sorting for the IMAP4 SORT Extension

Abstract

 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 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/rfc5957.

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.

Karp IMAP4 Display-Based Address Sorting [Page 1] RFC 5957 July 2010

Table of Contents

 1. Introduction ....................................................2
 2. Conventions Used in This Document ...............................2
 3. DISPLAY Sort Value for an Address ...............................2
 4. The DISPLAYFROM and DISPLAYTO Sort Criteria .....................3
 5. Formal Syntax ...................................................3
 6. Security Considerations .........................................3
 7. Internationalization Considerations .............................4
 8. IANA Considerations .............................................4
 9. Normative References ............................................4

1. 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 2010

7. 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.com

Karp IMAP4 Display-Based Address Sorting [Page 5]

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