For validating email, we create a user defined function named is_valid_email. You can paste this function to your php file and call the function wherever needed.
This function accepts two parameters, in which one is a default parameter, which we do not need to give value for that parameter. Another one parameter is email. While calling the function just supply the email to be verified as the first parameter. Second we can leave as blank.
function is_valid_email($email, $test_mx = false) {
if (eregi("^([_a-z0-9-]+)(\.[_a-z0-9-]+)*@([a-z0-9-]+)(\.[a-z0-9-]+)*(\.[a-z]{2,4})$", $email))
if ($test_mx) {
list($username, $domain) = split("@", $email);
return getmxrr($domain, $mxrecords);
} else
return true;
else
return false;
}