public function setIteratorFilter($mask = 0, $filter = null)
    {
        $this->_filter = array();

        if ($mask) {
            $this->_filter['mask'] = $mask;
        }

        if (!is_null($filter)) {
            $rfc822 = new Horde_Mail_Rfc822();
            $this->_filter['filter'] = $rfc822->parseAddressList($filter);
        }
    }