The Presence-ID Header Field
draft-saintandre-header-pres-00

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Abstract

This document defines a header field that enables the author of an email message to include a Presence URI in the message header block for the purpose of associating the author with an address that provides information about network availability, also known as "presence".

Table of Contents

1.  Introduction
2.  Syntax
3.  Implementation
    3.1.  Inclusion
    3.2.  Generation
    3.3.  Processing
    3.4.  Disposition
4.  IANA Considerations
5.  Security Considerations
6.  References
    6.1.  Normative References
    6.2.  Informative References
§  Author's Address
§  Intellectual Property and Copyright Statements

1.  Introduction

Several technologies enable entities to share information about their network availability, also known as "presence" [IMP‑REQS] (Day, M., Aggarwal, S., and J. Vincent, “Instant Messaging / Presence Protocol Requirements,” February 2000.). Such technologies include the Extensible Messaging and Presence Protocol [XMPP‑IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.) and the Session Initiation Protocol [SIP‑PRES] (Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” August 2004.). To facilitate the exchange of presence information, a URI scheme for presence is defined in [CPP] (Peterson, J., “Common Profile for Presence (CPP),” August 2004.).

Because almost all human users of presence systems are users of email systems, it can be helpful for such users to specify their presence URIs in the email messages they author. The Presence-ID header field provides a standard location for such information. This document documents the syntax and implementation of the Presence-ID header field, including the information necessary to register it in the Permanent Message Header Field Registry maintained by the IANA.

2.  Syntax

The syntax of the Presence-ID header field is defined below using Augmented Backus-Naur Form (as specified by [ABNF] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” October 2005.)), where the "PRES-URI" rule is defined in [CPP] (Peterson, J., “Common Profile for Presence (CPP),” August 2004.) and the remaining rules are defined in [MESSAGE] (Resnick, P., “Internet Message Format,” April 2001.):

"Presence-ID:" [FWS] PRES-URI *WSP CRLF

3.  Implementation

3.1.  Inclusion

The Presence-ID header field is associated with the author of the message; see [MESSAGE] (Resnick, P., “Internet Message Format,” April 2001.). If the "From:" header field contains more than one mailbox, the Presence-ID header field should not be added to the message. There should be no more than one instance of the Presence-ID header field.

3.2.  Generation

For a user whose presence URI is "juliet@example.com", the corresponding Presence-ID header field would be:

Presence-ID: pres:juliet@example.com

3.3.  Processing

Upon receiving an email message containing a Presence-ID header field, a mail user agent (MUA) that supports the field should process the field by resolving the presence URI in accordance with the procedures specified in [CPP] (Peterson, J., “Common Profile for Presence (CPP),” August 2004.).

3.4.  Disposition

A mail user agent (MUA) that has processed a Presence-ID header field may provide appropriate interface elements if it has independent information linking the author of the email message with the specified presence URI (e.g., via a user-controlled address book or automated directory lookup). If the user is subscribed to the presence of the author, such interface elements might include an indicator that the author is online and available for communication over a network.

4.  IANA Considerations

In accordance with [REG] (Klyne, G., Nottingham, M., and J. Mogul, “Registration Procedures for Message Header Fields,” September 2004.), the IANA registers the "Presence-ID" header field in the Permanent Message Header Field Registry. The registration template is as follows:

Header field name:

Presence-ID

Applicable protocol:

mail

Status:

permanent

Author/Change controller:

Peter Saint-Andre <mailto:stpeter@jabber.org>

Specification document(s):

draft-saintandre-header-pres-00 [Note to IANA and RFC Editor: Replace I-D name with RFC XXXX, where "XXXX" is the number of the RFC that results from this specification, if any]

Related information:

For detail information regarding presence URIs, refer to RFC 3859.

5.  Security Considerations

Message headers are an existing standard and are designed to easily accommodate new types. Although the Presence-ID header field may be forged, this problem is inherent in Internet email; however, because a forged Presence-ID header field may break automated processing, applications should not depend on the Presence-ID header field to indicate the authenticity of an email message or the identity of its author or sender. Including the Presence-ID header field among the signer header fields in DomainKeys Identified Mail (DKIM) can help to mitigate against forging of the header (see [DKIMSIG] (Allman, E., Callas, J., Delany, M., Libbey, M., Fenton, J., and M. Thomas, “DomainKeys Identified Mail (DKIM) Signatures,” May 2007.)).

Advertising presence URIs in email headers may make it easier for malicious users to harvest such URIs addresses and therefore to send unsolicited bulk communications to the users or applications represented by those addresses. Care should be taken in balancing the benefits of open information exchange against the potential costs of unwanted communication. An email user agent that is capable of including the Presence-ID header field in outgoing email messages should provide an option for its user to disable inclusion of the Presence-ID header field generally, on a per-recipient basis, and on a per-message basis.

The security considerations discussed in [URI] (Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax,” January 2005.) and [CPP] (Peterson, J., “Common Profile for Presence (CPP),” August 2004.) may also apply to the Presence-ID message header.

6.  References

6.1. Normative References

6.2. Informative References

Author's Address

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