How to validate non-english (UTF-8) encoded email address in Javascript and PHP?

Question

Part of a website I am currently working on contains registration process where users have to provide their email address. Just recently I became aware that non-ascii based

Answer 1

Attempting to validate email addresses may not be a good idea. The specifications (RFC5321, RFC5322) allow for so much flexibility that validating them with regular expressions is literally impossible, and validating with a function is a great deal of work. The result of this is that most email validation schemes end up rejecting a large number of valid email addresses, much to the inconvenience of the users. (By far the most common example of this is not allowing the + character.)

It is more likely that the user will (accidentally or deliberately) enter an incorrect email address than in an invalid one, so actually validating is a great deal of work for very little benefit, with possible costs if you do it incorrectly.

I would recommend that you just check for the presence of an @ character on the client and then send a confirmation email to verify it; it's the most practical way to validate and it confirms that the address is correct as well.