function check_email($mail_address) {
		if (preg_match("/^[0-9a-z]+(([\.\-_])[0-9a-z]+)*@[0-9a-z]+(([\.\-])[0-9a-z-]+)*\.[a-z]{2,4}$/i", $mail_address)) {
			return true;
		} else {
			return false;
		}
	}