PHP Function to validate an email address

Here is a simple Function to validate an email address in php.

function check_email($mail_address)

{

                        if($mail_address == '')

                        {

                                    return false;

                        }

                        else

                        {

if (preg_match("/^[0-9a-z]+(([\.\-_])[0-9a-z]+)*@[0-9a-z]+(([\.\-])[0-9a-z-]+)*\.[a-z]{2, 4}$/i",  strtolower($mail_address)))

                                    return true;

                        else

                                    return false;

                        }

}