284 lines
8.5 KiB
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284 lines
8.5 KiB
Plaintext
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Internet Engineering Task Force (IETF) D. Karp
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Request for Comments: 5957 Zimbra
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Updates: 5256 July 2010
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Category: Standards Track
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ISSN: 2070-1721
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Display-Based Address Sorting for the IMAP4 SORT Extension
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Abstract
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This document describes an IMAP protocol extension enabling server-
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side message sorting on the commonly displayed portion of the From
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and To header fields.
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Status of This Memo
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This is an Internet Standards Track document.
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This document is a product of the Internet Engineering Task Force
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(IETF). It represents the consensus of the IETF community. It has
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received public review and has been approved for publication by the
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Internet Engineering Steering Group (IESG). Further information on
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Internet Standards is available in Section 2 of RFC 5741.
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Information about the current status of this document, any errata,
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and how to provide feedback on it may be obtained at
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http://www.rfc-editor.org/info/rfc5957.
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Copyright Notice
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Copyright (c) 2010 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
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described in the Simplified BSD License.
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Karp IMAP4 Display-Based Address Sorting [Page 1]
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RFC 5957 July 2010
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Table of Contents
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1. Introduction ....................................................2
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2. Conventions Used in This Document ...............................2
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3. DISPLAY Sort Value for an Address ...............................2
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4. The DISPLAYFROM and DISPLAYTO Sort Criteria .....................3
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5. Formal Syntax ...................................................3
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6. Security Considerations .........................................3
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7. Internationalization Considerations .............................4
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8. IANA Considerations .............................................4
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9. Normative References ............................................4
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1. Introduction
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The [SORT] extension to the [IMAP] protocol provides a means for the
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server-based sorting of messages. It defines a set of sort criteria
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and the mechanism for determining the sort value of a message for
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each such ordering.
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The [SORT] FROM and TO orderings sort messages lexically on the
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[IMAP] addr-mailbox of the first address in the message's From and To
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headers, respectively. This document provides two alternative
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orderings, DISPLAYFROM and DISPLAYTO, which sort messages based on
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the first From or To address's [IMAP] addr-name (generally the same
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as its [RFC5322] display-name), when present.
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A server that supports the full [SORT] extension as well as both the
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DISPLAYFROM and DISPLAYTO sort criteria indicates this by returning
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"SORT=DISPLAY" in its CAPABILITY response.
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2. Conventions Used in This Document
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in [RFC2119].
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3. DISPLAY Sort Value for an Address
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For the purposes of the sort criteria defined in this document, the
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sort value for an [IMAP] address structure is defined as follows:
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o If the address structure's [IMAP] addr-name is non-NIL, apply the
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procedure from [RFC5255], Section 4.6. (That is, decode any
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[RFC2047] encoded-words and convert the resulting character string
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into a charset valid for the currently active [RFC4790] collation,
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with a default of UTF-8.) If the resulting octet string is not
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the empty string, use it as the sort value for the address.
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Karp IMAP4 Display-Based Address Sorting [Page 2]
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RFC 5957 July 2010
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o Otherwise, if the address structure's [IMAP] addr-mailbox and
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[IMAP] addr-host are both non-NIL, the sort value for the address
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is addr-mailbox@addr-host.
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o Otherwise, if the address structure's [IMAP] addr-mailbox is non-
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NIL, the sort value for the address is its addr-mailbox.
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o If none of the above conditions are met, the sort value for the
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address is the empty string.
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4. The DISPLAYFROM and DISPLAYTO Sort Criteria
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This document introduces two new [SORT] sort criteria, DISPLAYFROM
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and DISPLAYTO. A message's sort value under these orderings MUST be
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derived as follows:
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A "derived-addr" value is created from the [IMAP] envelope structure
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resulting from a FETCH ENVELOPE on the message. For DISPLAYFROM, the
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derived-addr value is the [IMAP] env-from value. For DISPLAYTO, the
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derived-addr value is the [IMAP] env-to value.
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o If the derived-addr value is NIL, the message's sort value is the
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empty string.
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o Otherwise, the message's sort value is the DISPLAY sort value of
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the first [IMAP] address in the derived-addr value.
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5. Formal Syntax
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The following syntax specification uses the Augmented Backus-Naur
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Form (ABNF) notation as specified in [RFC5234]. [IMAP] defines the
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non-terminal "capability", and [SORT] defines "sort-key".
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capability =/ "SORT=DISPLAY"
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sort-key =/ "DISPLAYFROM" / "DISPLAYTO"
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6. Security Considerations
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This document defines an additional IMAP4 capability. As such, it
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does not change the underlying security considerations of [IMAP].
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The author believes that no new security issues are introduced with
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this additional IMAP4 capability.
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Karp IMAP4 Display-Based Address Sorting [Page 3]
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RFC 5957 July 2010
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7. Internationalization Considerations
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DISPLAYFROM and DISPLAYTO are string-based sort criteria. As stated
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in [SORT], the active [RFC4790] collation as per [RFC5255] MUST be
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used when sorting such strings.
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The DISPLAYFROM and DISPLAYTO orderings sort on the full decoded
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[IMAP] addr-name, when present. They do not attempt to parse this
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string in a locale- or language-dependent manner in order to
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determine and sort on some semantically meaningful substring such as
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the surname.
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8. IANA Considerations
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[IMAP] capabilities are registered by publishing a Standards Track or
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IESG-approved Experimental RFC. This document constitutes
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registration of the SORT=DISPLAY capability in the [IMAP]
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capabilities registry.
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9. Normative References
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[IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
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4rev1", RFC 3501, March 2003.
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[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
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Part Three: Message Header Extensions for Non-ASCII Text",
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RFC 2047, November 1996.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet
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Application Protocol Collation Registry", RFC 4790, March
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2007.
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[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
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Syntax Specifications: ABNF", STD 68, RFC 5234, January
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2008.
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[RFC5255] Newman, C., Gulbrandsen, A., and A. Melnikov, "Internet
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Message Access Protocol Internationalization", RFC 5255,
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June 2008.
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[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
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October 2008.
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Karp IMAP4 Display-Based Address Sorting [Page 4]
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RFC 5957 July 2010
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[SORT] Crispin, M. and K. Murchison, "Internet Message Access
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Protocol - SORT and THREAD Extensions", RFC 5256, June
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2008.
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Author's Address
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Dan Karp
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Zimbra
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3401 Hillview Avenue
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Palo Alto, CA 94304
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USA
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EMail: dkarp@zimbra.com
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URI: http://www.zimbra.com
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Karp IMAP4 Display-Based Address Sorting [Page 5]
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