protected function list_thread_messages($folder, $page, $slice=0)
    {
        // get all threads (not sorted)
        if ($mcache = $this->get_mcache_engine()) {
            $threads = $mcache->get_thread($folder);
        }
        else {
            $threads = $this->threads($folder);
        }

        return $this->fetch_thread_headers($folder, $threads, $page, $slice);
    }