Is your fowarded email going through a single interaction queue? (email.foward-queue)
If yes, you could use java stat (look at stat server user's guide for more info) and use the stats on that interaction queue. Or, WDE is attaching UData when forwarding the mail, use StatServer Filters on that KVP. Another solution is at the strategy level, you can create a VQ (count) just to peg ixn on specific condition.