private function get_index_row($mailbox)
    {
        // Get index from DB
        $sql_result = $this->db->query(
            "SELECT `data`, `valid`"
            ." FROM {$this->index_table}"
            ." WHERE `user_id` = ?"
                ." AND `mailbox` = ?",
            $this->userid, $mailbox);

        if ($sql_arr = $this->db->fetch_assoc($sql_result)) {
            $data  = explode('@', $sql_arr['data']);
            $index = $this->db->decode($data[0], true);
            unset($data[0]);

            if (empty($index)) {
                $index = new rcube_result_index($mailbox);
            }

            return array(
                'valid'      => $sql_arr['valid'],
                'object'     => $index,
                'sort_field' => $data[1],
                'deleted'    => $data[2],
                'validity'   => $data[3],
                'uidnext'    => $data[4],
                'modseq'     => $data[5],
            );
        }

        return null;
    }