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Re: [ietf-smtp] Dombox - A Zero Spam Mail System

2019-10-06 19:40:57

--On Sunday, 06 October, 2019 10:34 -0400 Keith Moore
<moore(_at_)network-heretics(_dot_)com> wrote:

Well, at least for this specific proposal, the only place that
it matters whether the name is an IDN is whether the leftmost
facet of the name is not ASCII and therefore requires
encoding.   It won't confuse SMTP clients if other facets of
the name are non-ASCII.

Keith, I'm not sure what you are trying to say.  Except in EHLO
and the DNS itself, where, as John Levine pointed, A-labels are
required, SMTP won't allow _anything_ other than ASCII in any
domain name or mailbox address in the envelope with no
distinction between the leftmost label and any other one, unless
SMTPUTF8 is offered and accepted.  For applications using IDNA,
which include SMTP if SMTPUTF8 is in used, the IDNA specs
prohibit the use of any domain name label that starts with
letter-letter-hyphen-hyphen to allow for future extensions.  So,
if I understand the cases you are talking about above, they are
already prohibited.

My real point was, if you're going to encode something new in
a DNS name, try to avoid introducing dependencies on the way
that IDNs are encoded, because it's likely to bite back sooner
or later.

Right.  But the only case in which that could arise would
involve an application that did not support IDNA and that
happened to choose a label syntax that started with "xn--" or
even that used a letter-letter-hyphen-hyphen form for something
else and without updating the IDNA specs.  IDNA, at least in the
ACE form with that prefix, has been with us for close to 17
years now.   Certainly there are embedded applications that are
older than that which don't support (some of those are old
enough that they are still using HELO, and that is more than a
quarter-century).  Any contemporary application that invents a
new label prefix that looks like IDNA is almost certainly an
attack or someone being so clever as to amount to blatant


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