Mail_Mime issue

Hello, I'm using the PEAR;;Mail_Mime class to decode incoming Mails and extract the attachments. With normal Textfiles this works well, but if *.gz file are in and I try to extract them is only normal text what I receive. Example Code: function _getAttachments( $part ) {

       // check where we find the filename
       if ( $part->ctype_parameters['name'] ) {
           $filename = $this->_tmpdir.'/'.$part->ctype_parameters['name'];
       } else {
           $filename = $this->_tmpdir.'/'.$part->d_parameters['filename'];
       }
       // open filehandle
       $fh = fopen($filename, 'w+');
             // if encoded so decode and write down to file
       if ( $part->headers['content-transfer-encoding'] == 'base64' ) {
           fwrite($fh, base64_decode($part->body), strlen(base64_decode($part->body)));
       } elseif ( $part->headers['content-transfer-encoding'] == 'utf8' ) {
           fwrite($fh, utf8_decode($part->body), strlen(utf8_decode($part->body)));
       } else {
           fwrite($fh, $part->body, strlen($part->body));          }
       fclose($fh);
             // assign back to files array
       $this->_files[] = array('filename' => $filename, 'type' => 'attachment');

} An then I check the files and see: # file explorer.832ca1fc.spnb56-2004.04.13.08.38.tar.gz

explorer.832ca1fc.spnb56-2004.04.13.08.38.tar.gz:    ascii text

and not

explorer.832ca1fc.spnb56-2004.04.13.08.38.tar.gz:    gzip compressed data - deflate method , original file name

My params for Mail_mimeDecode class are: $this->_params = array(

                           'include_bodies'    => true,
                           'decode_bodies'        => false,
                           'decode_headers'    => true
                           );

What I'm doing wrong? thanks in forward. Cheers -Peter