protected function _pipeline($cmd = null)
    {
        if (!isset($this->_temp['fetchob'])) {
            $this->_temp['fetchob'] = new Horde_Imap_Client_Fetch_Results(
                $this->_fetchDataClass,
                Horde_Imap_Client_Fetch_Results::SEQUENCE
            );
        }

        $ob = new Horde_Imap_Client_Interaction_Pipeline(
            clone $this->_temp['fetchob']
        );

        if (!is_null($cmd)) {
            $ob->add($cmd);
        }

        return $ob;
    }