The easiest and safest way to check whether an email address is well-formed is to use PHP's filter_var () function. In the code below, if the e-mail address is not well-formed, then store an error message: $email = test_input ($_POST ["email"]); if (!filter_var ($email, FILTER_VALIDATE_EMAIL)) { $emailErr = "Invalid email format"; }

There are a few things you can do to check if an email address is invalid: Check the syntax Use Google Use an email finder tool like Findymail