How can I convert winmail.dat TNEF attachments to their original content?

sub filter {
  my($entity, $fname, $ext, $type) = @_;

  if (lc($type) eq "application/ms-tnef" or lc($fname) eq "winmail.dat" ) {
    use Convert::TNEF;
    use File::Type;
    use File::Temp qw(tempfile tempdir);

    my $tnefdir = tempdir(CLEANUP => 1, DIR => "/tmp");
    my $tnef = Convert::TNEF->read_ent($entity,{output_dir=>"$tnefdir"});

    my $ft = File::Type->new();

    for ($tnef->attachments) {
         my $mimetype = $ft->mime_type($_->data);

         my $tnef_entity = action_add_part($entity, "$mimetype", "base64", $_->data, $_->longname, "attachment");
         md_graphdefang_log('tnef_ext', "File: " . $_->longname . " Type: $mimetype");

         filter ($tnef_entity, $_->longname, "", "$mimetype");
    }
    $tnef->purge;
    return action_drop();
  }
  return action_accept();
}