protected function _encode($text)
    {
        $restore = mb_internal_encoding();
        mb_internal_encoding($this->_appCharset);
        if (empty($this->headerCharset)) {
            $this->headerCharset = $this->charset;
        }
        $return = mb_encode_mimeheader($text, $this->headerCharset, 'B');
        mb_internal_encoding($restore);

        return $return;
    }