Has anyone found that bouncing spam does any good at all, other than
telling the spammers that you really exist?
Bouncing with EXITCODE=<no such user> doesn't tell them that.
pseudo-bouncing with a rejection message may tell them that you exist, but
it also tells them that they don't want to do the work to get through to
you (especially since you have made it obvious that doing so WON'T make a
sale).
I pseudo-bounce most spam (being careful to avoid bouncing certain
types). I also (eventually) forward some of the spams to upstream ISPs
and (when applicable) to legal authorities. I have no way to determine
whether any of these actions is responsible, but I can say that the flow
of spam to me has gradually tapered off from several per day three months
ago to about two per week now.
I also have considerably changed my recipes and messages since I
downloaded Ariel's SpamBouncer.
As others have often warned, one must be careful lest innocent parties get
blamed for spam in these bounces. Spammers are not only thieves, but
forgers. However, in all this time, I have had less than half of my
bounces re-bounced, and received only one complaint about a misguided
bounce.
YMMV