private function renderTextAndHtml(&$content, $text, $html, $encoding, $boundary)
    {
        $uid = uniqid();
        $boundary2 = "x----_=_NextPart_003_$uid";
        $content .= "\r\n--$boundary\r\n";
        $content .= "Content-Type: multipart/alternative;\r\n\tboundary=\"$boundary2\"\r\n";
        $this->renderPlainText($content, $text, $encoding, $boundary2);
        $this->renderHtml($content, $html, $encoding, $boundary2);
        $content .= "\r\n--$boundary2--\r\n";
    }