Block No Reverse DNS

How do you setup Exim to refuse email from MTA's that do not have a valid 
reverse DNS?

I also heard of some hack that allowed you to look at a reverse DNS and if 
it contained *dial*, *dsl*, *cable*, *208-34-34-34*, *204.34.34.34* or 
something like that refuse it since it would likely be a dynamic IP pool. 
Anyone know the trick for that?

Using tricks like this about how much legitiment email do you think would be 
blocked?

Matt