[exim] Blocking From: <>

I have a few users that have a certain anti-junkmail software. It
supposeably bounces junkmail. The theory is that the spammer will get the
bounce and think the email address is no longer valid and remove it from
there list. I am so sure that happens. In reality most times the return
address is forged and goes to the wrong place.

Is there anyway to setup Exim so when it sees a return address of "<>" and
its not addressed to a local user or from exim itself refuse it?

Matt