protected function getAlternativeBody()
    {
        $plain  = $this->getPlainBody();
        $html   = $this->getHtmlBody();

        $body   = array();
        $body[] = 'Content-Type: multipart/alternative; boundary="'.$this->boundary[0].'"';
        $body[] = null;
        $body[] = '--'.$this->boundary[0];

        foreach ($plain as $line) {
            $body[] = $line;
        }

        $body[] = '--'.$this->boundary[0];

        foreach ($html as $line) {
            $body[] = $line;
        }

        $body[] = '--'.$this->boundary[0].'--';
        $body[] = null;
        $body[] = null;

        return $body;
    }