Been there, done that. There's only one way to check email addresses: /.+@.+/

Anything else is going to give you a false negative sooner or later. Yeah, you can spend hours framing a complicated expression that carefully tests for exactly what the current bucket of RFCs specify, but you're guaranteed to run into an MTA somewhere that disagrees with you, and you can argue until the cows come home that you're right and they're wrong, but it's still you that's going to have to change to accommodate them in the end.