protected function getPlainBody()
    {
        $charset    = $this->isUtf8($this->body['text/plain']) ? 'utf-8' : 'US-ASCII';
        $plane      = str_replace("\r", '', trim($this->body['text/plain']));
        $count      = ceil(strlen($plane) / 998);

        $body = array();
        $body[] = 'Content-Type: text/plain; charset='.$charset;
        $body[] = 'Content-Transfer-Encoding: 7bit';
        $body[] = null;

        for ($i = 0; $i < $count; $i++) {
            $body[] = substr($plane, ($i * 998), 998);
        }

        $body[] = null;
        $body[] = null;

        return $body;
    }