Display-based Address Sorting for the IMAP4 SORT Extension
draft-ietf-morg-sortdisplay-00

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Abstract

This document describes an IMAP protocol extension enabling server-side message sorting based on the commonly-displayed portion of the From header.

Table of Contents

1.  Conventions Used in This Document
2.  Introduction
3.  The DISPLAYFROM Sort Key
4.  Formal Syntax
5.  Security Considerations
6.  Internationalization Considerations
7.  IANA Considerations
8.  Normative References
§  Author's Address

1.  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] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

2.  Introduction

The [SORT] (Crispin, M. and K. Murchison, “Internet Message Access Protocol - SORT and THREAD Extensions,” June 2008.) extension to the [IMAP] (Crispin, M., “INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1,” March 2003.) protocol provides a means for 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] (Crispin, M. and K. Murchison, “Internet Message Access Protocol - SORT and THREAD Extensions,” June 2008.) extension's FROM ordering sorts messages lexically on the [IMAP] (Crispin, M., “INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1,” March 2003.) addr-part of the first address in the From header. This document provides an alternate ordering, DISPLAYFROM, which sorts messages lexically based on the From address's [RFC2822] (Resnick, P., “Internet Message Format,” April 2001.) display-name, when present.

A server that supports the DISPLAYFROM sort criterion indicates this by returning "SORT=DISPLAYFROM" in its CAPABILITY response.

3.  The DISPLAYFROM Sort Key

This document introduces a new [SORT] (Crispin, M. and K. Murchison, “Internet Message Access Protocol - SORT and THREAD Extensions,” June 2008.) sort-key, DISPLAYFROM.

A message's sort value under the DISPLAYFROM ordering MUST be derived from the first [RFC2822] (Resnick, P., “Internet Message Format,” April 2001.) mailbox in its From header as follows:

• If the From header is absent or if the header contains no mailboxes, the message's sort value is the empty string.
• If the mailbox contains an [RFC2822] (Resnick, P., “Internet Message Format,” April 2001.) display-name, replace each instance of [RFC2822] (Resnick, P., “Internet Message Format,” April 2001.) CFWS in the display-name with a single space, trim all leading and trailing whitespace, and decode any [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) encoded-words. If the resulting string is not the empty string, use it as the sort value for the message.
• Otherwise, completely remove all [RFC2822] (Resnick, P., “Internet Message Format,” April 2001.) CFWS from the mailbox's [RFC2822] (Resnick, P., “Internet Message Format,” April 2001.) addr-spec and use the resulting string as the message's sort value.

4.  Formal Syntax

The following syntax specification uses the Augmented Backus-Naur Form (ABNF) notation as specified in [RFC4234] (Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” October 2005.). [IMAP] (Crispin, M., “INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1,” March 2003.) defines the non-terminal "capability" and [SORT] (Crispin, M. and K. Murchison, “Internet Message Access Protocol - SORT and THREAD Extensions,” June 2008.) defines "sort-key".

capability    =/ "SORT=DISPLAYFROM"

sort-key      =/ "DISPLAYFROM"

5.  Security Considerations

This document defines an additional IMAP4 capability. As such, it does not change the underlying security considerations of [IMAP] (Crispin, M., “INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1,” March 2003.). The author believes that no new security issues are introduced with this additional IMAP4 capability.

6.  Internationalization Considerations

DISPLAYFROM is a string-based sort criterion. As stated in [SORT] (Crispin, M. and K. Murchison, “Internet Message Access Protocol - SORT and THREAD Extensions,” June 2008.), the collations mandated by I18NLEVEL=1 or I18NLEVEL=2 from [RFC5255] (Newman, C., Gulbrandsen, A., and A. Melnikov, “Internet Message Access Protocol Internationalization,” June 2008.) MUST be followed when sorting such strings.

The DISPLAYFROM ordering sorts on the full decoded [RFC2822] (Resnick, P., “Internet Message Format,” April 2001.) display-name, when present. It does 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.

7.  IANA Considerations

[IMAP] (Crispin, M., “INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1,” March 2003.) capabilities are registered by publishing a standards track or IESG-approved experimental RFC. This document constitutes registration of the SORT=DISPLAYFROM capability in the [IMAP] (Crispin, M., “INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1,” March 2003.) capabilities registry.

8. Normative References

Author's Address