Dec. 29, 2017
3:48 p.m.
Punycode is just ASCII text, and ASCII text is certainly valid in the local part of an address. A mailbox like xn--ls8h is just as valid as any other. The fact that it happens to look like an A-label is a concidence.
This matches my understanding. Some people on this list appear to think that SMTP servers ought to consider punycode in the domain part as equivalent to utf8, though. Arnt