Re: [EAI] double angle brackets

[John C Klensin <klensin at jck.com>]

--On Tuesday, September 08, 2009 16:51 +0000 Shawn Steele
<Shawn.Steele at microsoft.com> wrote:

>> To replace double angle brackets for the Sender, John Klensin
>> proposed  using multiple From fields. SM amended this with
>> Reply-To to specify the  preferred address, as in
>>         From: EAI-addr, ASCII-addr
>>         Reply-To: EAI-addr
>> where the EAI-addr gets dropped in Downgrade.
> 
> I'd imagine that "something" isn't going to be happy with 2
> addresses.

Right.  In particular, there are a lot of systems that do not
support multiple-address From:, multiple-address Reply-to:, or
both.

> It seems to me that 99% of the time email can be viewed as
> primarily "sender side" or "recipient side".  Eg: Mail goes
> from a sender system to a recipient system.  It is very rare
> (now) that an in-between system would relay mail from an
> untrusted server to another 3rd party server.  If there is a
> relay, it'd have to trust the sender, so it's pretty much
> "sender side," or recognize the recipient "recipient side."
> 
> Assuming that a "sender" has an EAI aware system that is
> completely conformant and "works" with UTF-8 addresses, then
> the entire "sender side" would have to be updated to support
> UTF-8 addresses.  If the sender's relays aren't upgraded, then
> all of their mail ends up being downgraded anyway.
> 
> Similarly a recipient either has an entirely EAI aware system,
> or they don't.  
> 
> So I'm wondering how interesting downgrade really is.  If my
> sending system trusts the sender, presumably it could request
> an ASCII address from the trusted sender-side server if it
> needed to downgrade.  (Through some other mechanism, like
> asking the trusted server what other aliases were valid for
> that account using some new, or even proprietary, protocol).

This is the "do we really need downgrade" argument that some of
us have been raising on and off for years.  The answer has never
been "yes" or "no" but "are there enough edge cases (that do not
conform to the analysis) out there to make downgrading useful
anyway, at some cost level".   If anything has changed recently
it has been either

	* a perception that there are fewer relevant cases where
	downgrade is actually needed than was originally
	believed.
	
	* a perception that the costs and risks of having a
	downgrading arrangement (e.g., with double angle
	brackets) make the number of relevant cases needed to
	justify the mechanism much larger than we had originally
	believed.

Of course, both may be true, but would make the case for "no
downgrade" even more open and shut.

> So the proposed solution seems like overkill.
> 
> VERY worst case a client (like Outlook) can try to send an EAI
> email.  If it bounces, the client could resend using my ASCII
> address (assuming it is properly configured).  It could even
> do that silently, or with maybe a little warning saying that
> had been downgraded.

That, of course, means that it knows your ASCII address.  Absent
some configuration changes, it might not.

But I think we are in violent agreement, or at least getting
close to it.

    john