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 domains are possible (so is email).
My backend is utf-8 encoded MySQL where I am expecting any users (with differnt locales) should be able to enter their email but don’t know how to validate this kind of email address.

Currently I am testing out jquery tools and it validates the english email address correctly but fails to validate non ascii email. Also I need to do same at server side with php. Is there a regular expression that can validate this kind of email address?

I have tried this but it fails in jquery tools (this is just example for demo, I don’t understand this too)

闪闪发光@闪闪发光.com

Also what will happen when they type their English email address ([e-mail]) with their own IME. Can this be validated with current regular expression we have for English mail validation. Currently I don’t have to worry if that email exist for not.

Thanks

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.