Email address validation is basically an impossible problem. In practice, the best strategy is: 1. Check if email is wellformed, with an *extremely* lenien

Email address validation is basically an impossible problem. In practice, the best strategy is: 1. Check if email is wellformed, with an *extremely* lenient algorithm. Basically, do we have .*@.* ? 2. Check that the domain is real, has an MX record, and the SMTP server in the MX record exists. Ok, send mail! The only way to verify after that is to send an email with a verification link and complete the circle.