Internationalised domain names are supported: as I mentioned, the spec explicitly reminds you to do punycode. For the local part, though, it does look like bro

Internationalised domain names are supported: as I mentioned, the spec explicitly reminds you to do punycode. For the local part, though, it does look like browsers have fallen down, though I’m not particularly familiar with the situation there. Testing it in Firefox to confirm, ascii@υνικοδε validates, but υνικοδε@ascii doesn’t. https://github.com/whatwg/html/issues/4562 https://github.com/whatwg/html/issues/4562 seems to be where progress is made from time to time. As usual, it’s not as simple as we might hope.