On 10/6/19 10:14 AM, Arnt Gulbrandsen wrote:
On Sunday 6 October 2019 14:13:38 CEST, Keith Moore wrote:
Regarding the use of IDNs, the easiest way to address this is to not
use IDNs as the targets of MX records - since users don't generally
see the MX records anyway.
Which is a good idea for another reason — the MX target is generally
the same as or similar to the name used as EHLO argument, and EHLO is
issued before the sender knows whether the received supports SMTPUTF8.
I can't find any justification at all for ever using the UTF-8 form of
an IDN in EHLO. IMO it should be a MUST NOT.
But I don't know whether it's reason enough to get a non-IDN domain.
IMO it's reason enough to use a non-IDN domain for mail servers if one
has such a domain, but registering another domain? maybe not. And for
that reason, perhaps not something that can be advised in an RFC.
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.
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.
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