public function getEncodedStream()
    {
        if (!$this->_isStream) {
            // require_once 'Zend/Mime/Exception.php';
            throw new Zend_Mime_Exception('Attempt to get a stream from a string part');
        }

        //stream_filter_remove(); // ??? is that right?
        switch ($this->encoding) {
            case Zend_Mime::ENCODING_QUOTEDPRINTABLE:
                $filter = stream_filter_append(
                    $this->_content,
                    'convert.quoted-printable-encode',
                    STREAM_FILTER_READ,
                    array(
                        'line-length'      => 76,
                        'line-break-chars' => Zend_Mime::LINEEND
                    )
                );
                if (!is_resource($filter)) {
                    // require_once 'Zend/Mime/Exception.php';
                    throw new Zend_Mime_Exception('Failed to append quoted-printable filter');
                }
                break;
            case Zend_Mime::ENCODING_BASE64:
                $filter = stream_filter_append(
                    $this->_content,
                    'convert.base64-encode',
                    STREAM_FILTER_READ,
                    array(
                        'line-length'      => 76,
                        'line-break-chars' => Zend_Mime::LINEEND
                    )
                );
                if (!is_resource($filter)) {
                    // require_once 'Zend/Mime/Exception.php';
                    throw new Zend_Mime_Exception('Failed to append base64 filter');
                }
                break;
            default:
        }
        return $this->_content;
    }