I have an external-reference type in mind which would be handled by an
MTA or UA and which would provide access to messages.
For instance, I have on hand a message to which I am responding or
which I am announcing availablity for retrieval. I might include an
Message/External-body body part like
Content-Type: message/external-body;
name="<id(_at_)some(_dot_)dom(_dot_)ain>";
access-type="message-retrieval";
address="david(_at_)twg(_dot_)com"
For instance, there is a References: header available which contains
Message-ID:'s of messages to which this one refers. A user agent may
want to provide a way to easily retrieve and display those messages.
If it keeps track of which messages it has, and the referenced message
is directly available, then this is easy. Otherwise it might keep a
list of message-ID's it has seen along with originator-addresses, and
for such a message the retrieval would take a little while.
Now, how to do the query to retrieve the message? A mechanism which
comes to mind is along the lines of the Control: field in Usenet
messages. Namely, some usenet messages perform control functions
instead of disseminating information. These messages all contain a
Control: header. There is a defined format for the contents of control
messages, roughly speaking the first "word" is a `command' as to what
to do. These include creating or deleting newsgroups, deleting
messages, retrieving system information (version's, and the `sys' file)
and lastly retrieving messages.
I can easily justify two control messages for a UA. These are
MIME-Control: sendversion
and MIME-Control: sendme <id(_at_)some(_dot_)dom(_dot_)ain>
or
Content-Type: control/sendversion
and Content-Type: control/sendme;
message-id="<id(_at_)some(_dot_)dom(_dot_)ain>"
`sendversion' returns a message describing the `name' of the
user agent and it's `version' number. The intended use is for
system administrator use -- they have a problem with keeping
software to date y'see. With this `sendversion' capability
they are able to query all UA's they care about and find out
what is out there. It`s probably worth the bother to define
a nice format for containing the name & version information,
but probably isn't worth the bother to define a list of Accepted
and Approved names or versions.
`sendme' is borrowed from Usenet and implements the above stuff.
It would look for the message and return it to the address
listed in the From: or Reply-To: lines. A "negative retrieval report"
type of message should be defined. The retrieved message might
have a special Content-Type: of control/retrieved-message ...
(Or Content-Type: message/retrieved-message).
None of this is seriously suggested or intended for the
finalization of RFC-MIME. It should probably be in RFC-CONTROL
instead ;-).
While the title of the RFC says "multi-media" at least half the
justification of this effort is to extend the utility and power of
e-mail. Having a `sendme' capability does a *lot*. It would be
even *more* powerful if there were a way to retrieve Usenet/NNTP articles
with a `sendme' or an external-body mechanism. Especially if/when
the Usenet folk start incorporating some RFC-MIME features.
David