[Exim] dump undeliverable incoming

Hi list:

After an hour of research, I'm ready to ask:

What I want to do is DROP all incoming messages destined for non-existent
users (i.e. noSuchUser@???). I use the ignore_errmsg_errors to deal
with message that are routable, but undeliverable.
But what about spam bounces that are unroutable, undeliverable,
uneverything. They still stagnate in my queue.

I realize this isn't the 'polite' thing to do for senders that 'typo' our
valid email names, but we get WAY MORE SPAM than not.

As a perfect solution, can I set my Exim (v3) to bounce a failed local
delivery, but DUMP any failed bounces (for any reason)?

-with thanks
Mike Scott