Steps to reproduce:

Copied from https://bugzilla.mozilla.org/show_bug.cgi?id=618876, which was closed once the domain part of the bug was resolved:

input@type=email doesn't seem to support IDNs, for example the valid address "Max.Müller@example.org" isn't accepted as a valid mail address due to the u umlaut. However, that string is a valid e-mail address and addresses like this get used more and more. ...

Actual results:

input type=email flags the ü as invalid and the form cannot be submitted. ü is accepted in the domain, but not in the localpart.

Expected results:

ü should have been valid as far as the browser is concerned. A lot of servers aren't able to send mail to max.müller@..., but a bigger lot of servers are able to do it.

It's not representative of the whole world, but earlier this month I investigated the EAI support for aau.org (the Association of African Universities) in connection with a workshop there. A little over 73% of the universities were able to send mail to EAI addresses.

This could be regarded either as a defect or as a request for enhancement. Few people have such email addresses, so I lean towards the latter. Anyway I made a PR to fix it: https://phabricator.services.mozilla.com/D176259

This was fixed for domains in 2011 as part of fixing bug 618876; this patch adds support for unicode in localparts.

https://github.com/whatwg/html/issues/4562 contains relevant discussion.

(Note that punycode is only defined for domains; you're not permitted to
assume anything about other people's localparts. In particular you're not
permitted to assume that grå@... is equivalent to xn--gr-zia@...)

The Bugbug bot thinks this bug should belong to the 'Core::Networking' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Sorry about the wrong component.