IIR (I have not gone back and reread the spec), conversion of
the domain name to A-labels is strongly discouraged at any point
prior to the MSA or MTA actually looking up the domain name so a
connection can be opened. For message headers (including not
just the "From:" header field but trace fields, etc.), it is
even more strongly discouraged: the intent was "restricted UTF-8
all the way" and "making users look at A-labels is just looking
for trouble". However, the intent with IDNA (and, I think, the
push for IRIs) was much the same, keeping internal forms and
users separated and the latter working with native-character
forms to the extent possible. However, the specs recognized
that exceptional circumstances could arise and therefore stop
short of complete prohibitions.
I haven't thought it through but, somehow, converting domains in
backward-pointing addresses (what do they do to/with
"Reply-to:"?) seems more, rather than less, offensive than
So, again relying on memory, the behavior you describe is in bad
taste and almost certainly represents bad judgment, but may not
actually be non-conforming. I'll leave the question of how far
on that spectrum an implementation needs to lie to be considered
--On Saturday, June 20, 2020 14:54 -0400 John R Levine
I am poking at the widely used Roundcube web mail package.
One of my test addresses is 测试@电子邮件测试.中国
When I enter it into Roundcube as a username, it turns the
domain into a-labels,
测试@xn--5nqx41au4nqohsp3axcg.xn--fiqs8s and uses that as
the address in the From: line, and to authenticate to IMAP and
submission. I can understand where that came from, but it
still seems wrong.
Addresses that I put on the To: line seem unmolested.
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks,
Please consider the environment before reading this e-mail.
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