Steve Atkins wrote:
Exim doesn't downgrade. It doesn't advertise 8bitmime either, by default.
If you switch on 8bitmime advertising, it still doesn't downgrade. I
think it just tries to deliver the mail as 8bit, regardless of what the
receiving MTA does. I think postfix and sendmail do the same, but I'm
not sure.
Exchange advertises 8bit and then bounces the mail if it tries to forward it
to a server that doesn't advertise 8bit.
This (entirely RFC valid yet completely broken) behaviour has bitten me
a couple of times.
+1
If everyone (mail transport/mail handlers) just followed the basic
mail networking principle of:
Thou should not touch passthru mail (except for network traces)
We would not be having these "side" issues today. There are legit
reasons for transformations but mainly at the final destination (local
routing).
The 8BITMIME thing is ideal to tell MUA/MTA (at the Interactive Level)
what is not acceptable at the MSA. So if the USER has 8bit enable in
his UI, then he can switch it to 7bit compatible format. But its
create problems when there is a "Mind Guessing" game between
intermediaries.
I'm not sure any of this affects DKIM much, other than "Hey, look! Yet
another way DKIM signatures might get removed in transit!".
The only solution I see for DKIM is to use Target/Path dependency
methods, but in principle, intermediaries need to refrain from
thinking they know better for downlinks.
hmmm, perhaps "DKIM Scouts" :)
--
Hector Santos, CTO
http://www.santronics.com
http://santronics.blogspot.com
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