The Presence-ID Header Field

This document defines a header field that enables the author of an email
or netnews 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".
Several technologies enable entities to share information about their
network availability, also known as "presence". Such technologies include
XMPP-IM (Extensible Messaging and Presence Protocol (XMPP): Instant
Messaging and Presence) and the Session Initiation Protocol (SIP). To
facilitate the exchange of presence information, a URI scheme for
presence is defined in Common Profile for Presence (CPP). Because almost
all human users of presence systems also use email systems and because
many such users also use netnews systems, it can be helpful for such
users to specify their presence URIs in the messages they author. The
Presence-ID header field provides a standard location for such
information. This memo 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. The Presence-ID header field is associated with the author of the
message. 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. Upon
receiving a message containing a Presence-ID header field, a user agent
that supports the field should process the field by resolving the
presence URI in accordance with the procedures specified in CPP. A user
agent that has processed a Presence-ID header field may provide appropriate
interface elements if it has independent information linking the author
of the 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. More Information