You shouldn't just look at the subject and sender headers... look at the others too. It may be that you can filter on the X-MIME-type or something.
If the from address is really just random characters then you could filter on "all from addresses not containing exactly one @ and at least two . " or something like that. (This is trivial to do in Eudora or Turnpike - not sure if Outlook is up to it).