public static function isEmail($email) {
        if (!is_string($email) || strlen($email) > 255)
            return false;
        if (Tools::phpVersionCompareTo('5.3.3') >= 0)
            return (boolean) filter_var($email, FILTER_VALIDATE_EMAIL);
        else
            return (boolean) preg_match('`^(?!\.)[.\w!#$%&\'*+/=?^_\`{|}~-]+@(?!-)[\w-]+\.\w+$`i', $email);
    }