After running into several web application that rejected any e-mail address on the new gTLDs because the apps were badly written to validate with a hard-coded list of valid TLDs, I wrote a e-mail validation function that I *think* does things properly. Free for anyone to use who wants to. https://deviant.email/emailaddytest.phps What it really does is use the PHP built-in filter_var but it compensates for known bugs in the filter_var e-mail address validation. It return boolean. I *think* it will properly validate any legal routable address and reject any that are not. But bugs may exist. By default when the host part of user at host is a domain name, it does a DNS query to validate the host resolves. That adds a little latency but I think is worth it. My own implementation will probably cache a positive result for up to 24 hours with APCu but that's not in the function linked. The dns lookup can be disabled. By default it will reject IP address as the host part, but that can be enabled. When enabled, it will reject private and reserved range. Well, reject what is hard-coded into PHP filter_var - I haven't tested that. International domain names will only validate if the php-intl functions are installed (to turn them into punycode) -=- For the username validation, that's where any bugs are most likely to exist. But I think I did it right. It's very unfortunate that the built-in php filter doesn't do it right. Anyway free for anyone, I'm tired of e-mail address filters that don't properly work with common user names on perfectly legal domains that just happen to be newly ICANN approved. You can see live testing by just removing the last s from the filename.