As somebody else said, don't. If you really feel you need some kind of validation, have two email fields so the user can enter it twice and double check it the

As somebody else said, don't. If you really feel you need some kind of validation, have two email fields so the user can enter it twice and double check it themselves. No matter how much effort you put into it, and how complicated your validation code is, if the users want to mess with you, they can always just enter a valid fake address, so there's no point wasting a lot of energy on it because it's easy to defeat anyway. And since it's impossible to validate addresses with a regular expression, there's a small chance you'll reject a valid address and look dumb.