There's probably a "misconceptions people have about e-mail addresses" post out there somewhere; the tl;dr is that so much is or will be allowed, for validation you should really only check if there's an @ in the address, for the rest just try to send an email and see if it bounces.

But don't activate an account without e-mail verification. I got a random account on Deezer because someone signed up with my e-mail address; they probably got it off a spam list. But it kind of implies that Deezer didn't do e-mail verification before letting people use their platform.