[Mailman-Users] Trapping messages with null subjects sent to list

[vancleef at lostwells.net]

Is there a recipe to put in the spam filters that will trap a totally
empty subject line in a message?   This get posted to a list with 
(no subject) in the subject line, but this is evidently added after
the spam filter check.  

I've tried \n, which catches these, but it also catches too many 
responses where the responder has changed the original subject as
well.  

Virtually all of these null-subject posts we get are demands to
unsubscribe the poster.  On our lists, we'd settle for catching them
as administrative requests.  

Hank