On Fri, 09 Jan 2009 15:31:57 -0000, John C Klensin <klensin(_at_)jck(_dot_)com>
Now, if what you are really asking about is my personal
opinion... At this point, I believe we would be better off
* without Downgrade as specified
* pushing for rapid implementation and deployment of an
internationalized email solution that is free of
in-transit downgrading and the associated syntax,
header, digital signature, etc., issues
* concentrating our efforts on address downgrading
procedures that could be applied at the endpoints --
the sending MUA or submission MTA and after SMTP final
delivery, rather than figuring out how to make
* getting more specific about the cases in which
in-transit downgrading might be needed and how they can
best be avoided by careful configuration.
Yes, that is a situation we can hope to arrive at eventually, but perhaps
not so soon as you seem to imply. For sure, there would have been huge
outcries if we had tried to introduce it with no downgrading right from
the start, so we had to do it that way. What happens next will depend on
how successful and how widely adopted implementation turns out to be. and
we shall not know that for a few years yet. But it would probably be
useful to mention in some document somewhere that there is an intention
that downgrading can eventually be phased out.
MIME got itself into a mess when it invented 8BITMIME, by saying that
implementations offering it MUST downgrade to 7bit if the next hop does
not advertise that extension. BUT, in practice, you would be hard pressed
nowadays to find a working server that was NOT 8-bit clean, at least for
bodies (and even 8bit cleanliness in headers is becoming near-universal).
But, of those 8-bit-body-clean implementations, some do not offer the
downgrqde service and, of those, some still advertise 8BITMIME rergardless
(e.g. qmail), whereas others (e.g. EXIM) refrain from advertising it
(though EXIM does allow individual admins to override that restraint).
The result of all that, as it turns out, is that 8bit stuff propagates
just fine, even via qmail, except that much unnecessary downgrading to
7bit takes place on account of implementations like EXIM which do it but
don't advertise it. And this unnecessary downgrading brings its own
problems, such as failure of s-MIME and DKIM signatures. Indeed, there is
just too much Q-P and base64 stuff flowng around these days, most of it
not really necessary.
So we need some sort of "sunset" clause that indicates that this state
will not last for ever. But at least, with IMA, we have quite properly
arranged that bouncing is an acceptable alternative to downgrading, and
this may well lead to the development of large cimmunities within which
downgrading is not provided, and I have no problem with that.
Charles H. Lindsey ---------At Home, doing my own thing------------------------
Tel: +44 161 436 6131
Email: chl(_at_)clerew(_dot_)man(_dot_)ac(_dot_)uk Snail: 5 Clerewood Ave, CHEADLE, SK8 3JU, U.K.
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