public function setHtmlBody($body, $charset = null, $alternative = true)
    {
        if (!$charset) {
            $charset = $this->_charset;
        }
        $this->_htmlBody = new Horde_Mime_Part();
        $this->_htmlBody->setType('text/html');
        $this->_htmlBody->setCharset($charset);
        $this->_htmlBody->setContents($body);
        if ($alternative) {
            $this->setBody(Horde_Text_Filter::filter($body, 'Html2text', array('charset' => $charset, 'wrap' => false)), $charset);
        }
        $this->_base = null;
    }