One other question. How do you manage domain based reputation vs IP reputation. I'm trying to get by running a service off of Cloud provider IPs and they may rotate from time to time as VPSs rotate. Part of me feels that once my domain has enough reputation it should be fine. It does seem like some of the big providers work like this (Google seems to trust me now from any IP) but it seems that a lot of smaller providers rely on blacklists more as they don't see as much traffic to build reputation. How do blacklists handle domain reputation?