PHP Email Validator – Email MX DNS Record Check

Validating an email address is one of the hardest feats on the web. A valid email can be marketing gold, but an invalid email address is dead weight. Not only does it require a CPU-taxing PHP regular expression ("/^[A-z0-9.-]+"."@" . "[A-z0-9][A-z0-9-]*". "(.[A-z0-9-]+)*".".([A-z]{2,6})$/"), the regular expression can be useless even after it's validated for format if the domain doesn't exist.

A regular expression simply wont do -- we need to think more low-level. What does email at any domain require? A DNS MX record. Well, PHP provides a great solution to validate that there's a MX record for the provided email address' domain.