[nine_k]

As long as you can receive a confirmation email, any address could work :)

But basic \S+@\S+ check on the UI side won't hurt and would be courteous.

[nightpool]

But what if I worked at stripe and only wanted to type my username? :D

[hackmiester]

On this form it's less relevant, but that's very handy a lot of the time. I get frustrated when some outsourced app seems to believe that just sending mail to my username would not work, and refuses to let me do it.