I just sent a patch to another mailing list, via the "Attach file as
mime" menu item in xemacs, pgnus 0.95.  The maintainer is getting a
mime error.

Attached are his message with all his headers and the message I
sent (also attached via the menu). 

I used the default application/octet-stream; would it have helped if I 
had used something more specific? (It was a .gz file.)