[Exim] ignore_bounce_errors and massive mailq...

I'm getting nailed with spam that is clearly on a dictionary to one of
my domains. Pretty much every attempt fails, and an error messages is
sent out. I've set:

ignore_bounce_errors_after = 2h

and tried:

ignore_bounce_errors

to try and get read of these notifications. I now have 26000+ messages
in my queue, and while I can get rid of them easily with:

exim -Mrm $(mailq | grep "<>" | awk '{print $3}')

I'd rather not have them to be begin with.

I'm working at a method of stopping the incoming mail at the gateway
(the messages are ultimately being bounced on the internal mail server
after passing in) but I've not yet had a chance to upgrade the gateway.
The internal server is running Exim 4.2, and I'd like some advice on
getting rid of these errors...

Chris