> It would likely be a good idea to block IP's in this list from using > authenticated SMTP to relay not?
Definitely not. We did so one week for testing. And had a lot of trouble with customers espacially using mobile/smartphones. Don't do this. This rbl does only make sense if you have different servers for receiving from external and for customer access. Then - only then - you this list makes sense on external receiving smtp servers, but never on hosts with authenticated customer access.
