Not sure how definitive this is... /^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/

Specifically, from bug 571897 comment 70: >+ onEmailChange: function () { >+ let re = .... Yuck. Email regex checking is something people almost always get wrong. I'm _hoping_ this came from some definitive source as wasn't just invented ad hoc. Should have a comment here noting it's provenance. Followup for investigating this?

It wasn't invented ad hoc. I dug it out of the internet somewhere last summer, but I don't have the link handy. It's been shipping to users for over a year (also used on the registration server side) and it seems to pass every test anyone's thrown at it.

One issue regarding the unicode in email addresses has popped up, filed bug 596233. Resolving based on mconnor's comment.