I'm not an exchange expert at all but you should be able to block requests to/from them at your router based on their server IP. Basically meaning instead of them eating your bandwidth up by their tarpit telling the spam server (you) to send very small packets you have zero communication with them.
I think Access control lists may be a solution for this but to be honest I'm not sure I'm just tossing my best guess out there.
One of the reason your ip will be blocked is because of sending spam or viruses, may be it's not you or your exchange, it could be a trojan on one of the computers in your network.
So how to know which one? you should block port 25 out from your network to internet, then no one can send email and hence no spam.
If you want users inside your network to be able to send email then you can setup an exchange server as smtp relay with proper Anti spam and anti virus.
And if you want to know who (which ip) are sending spams then you should use some kind of monitoring for port 25 out from your network.
Look at the link below (PDF) and see recommendations there.