PHP validate email

function isValidEmail($email){
return eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$", $email);
}

$email=mysql_real_escape_string($_POST['email']);
if (isValidEmail($email)==true) echo "OK";
if (isValidEmail($email)==false) echo "Not Okay";
?>