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.
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.
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