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Re: SMTP Service Extension for Priority

2001-06-26 01:39:15

Well first - thanks for all the comments!

If I can take a few of them in turn, and perhaps explain the
background a little. 

We do a lot of work with military systems, and they make use of
priority a great deal. They have different grades of messages from
routine traffic all the way up to FLASH priority ("ATTACK NOW!"). They
also have grades of service based on the precedence (like 3 minutes max
for delivery of a flash message). Under certain conditions they invoke
MINIMIZE conditions whereby only important traffic is allowed through
(to relieve congestion etc), so all traffic below a certain priority
will be ignored/saved/left unprocessed until the restriction is
lifted. Finally, different priorities (military call them precedences)
can be assigned to a messages To and CC recipients (maybe High
priority for To, and low for CC for instance).

Anyway - with that background, this extension allows the chance to
pass on the priority at a place in the protocol sufficient to make
full use of it. 

To respond to the comments...

AUTH may well be required to act on the priority - but that is really
down to the local setup. I don't think its something that should be
dictated.  If I wish to honor the protocol at this MTA for all, then
that is allowed (though maybe unwise). Likewise, if I wish to ignore
the priority from all connections except one, that is also allowed by
the draft. Section 7 does hint that you may need to do some of this.
In certain closed environments you may trust all connections and act
on the priority passed. Out on the wild internet, you will probably
only act on it from a few trusted connections (though see closing

If a client asserts a priority that the MTA dislikes, then it may take
several actions, including ignoring the request, or bouncing the
message, or just reverting to what it would do if no request was

When a message is relayed, it is down to the MTA what it may pass
on. It may just pass on the incoming priority, it may pass on its own
notion of priority or may not pass on anything. Obviously in a
cooperative environment, it would use and pass on the incoming
priority, subject to any AUTH checks.

As others have said, priority and importance are somewhat linked, but
not completely. You can come up with (somewhat contrived) examples of
high priority, low importance; and low priority, high importance

So really the draft is aimed at MTA to MTA traffic. The receiving UA
would be unaware of the priority that it was transfered with, though
might be able to deduce from other fields what it might have been.

In the military environment, this maps extremely well to service
extensions in use there. In the commercial environment, I can see it
being used in a variety of ways, mostly in localised enclaves though,
such as ISP routing their customer traffic ahead of other traffic
maybe, or providing grades of service for a fee. 

Use in the wild untamed internet I suspect will be more minimal,
although I could see low priority traffic being acted on. e.g., any
priority request above normal, we'll ignore, but we will respond to
requests for low priority processing - thus allowing bulk mail/dist
list processing to be passed on in a well defined way.


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