protected function _buildBody()
    {
        if (($text = $this->_mail->getBodyText())
            && ($html = $this->_mail->getBodyHtml()))
        {
            // Generate unique boundary for multipart/alternative
            $mime = new Zend_Mime(null);
            $boundaryLine = $mime->boundaryLine($this->EOL);
            $boundaryEnd  = $mime->mimeEnd($this->EOL);

            $text->disposition = false;
            $html->disposition = false;

            $body = $boundaryLine
                  . $text->getHeaders($this->EOL)
                  . $this->EOL
                  . $text->getContent($this->EOL)
                  . $this->EOL
                  . $boundaryLine
                  . $html->getHeaders($this->EOL)
                  . $this->EOL
                  . $html->getContent($this->EOL)
                  . $this->EOL
                  . $boundaryEnd;

            $mp           = new Zend_Mime_Part($body);
            $mp->type     = Zend_Mime::MULTIPART_ALTERNATIVE;
            $mp->boundary = $mime->boundary();

            $this->_isMultipart = true;

            // Ensure first part contains text alternatives
            array_unshift($this->_parts, $mp);

            // Get headers
            $this->_headers = $this->_mail->getHeaders();
            return;
        }

        // If not multipart, then get the body
        if (false !== ($body = $this->_mail->getBodyHtml())) {
            array_unshift($this->_parts, $body);
        } elseif (false !== ($body = $this->_mail->getBodyText())) {
            array_unshift($this->_parts, $body);
        }

        if (!$body) {
            /**
             * @see Zend_Mail_Transport_Exception
             */
            // require_once 'Zend/Mail/Transport/Exception.php';
            throw new Zend_Mail_Transport_Exception('No body specified');
        }

        // Get headers
        $this->_headers = $this->_mail->getHeaders();
        $headers = $body->getHeadersArray($this->EOL);
        foreach ($headers as $header) {
            // Headers in Zend_Mime_Part are kept as arrays with two elements, a
            // key and a value
            $this->_headers[$header[0]] = array($header[1]);
        }
    }