Reverse DNS lookup on IP requests.
When the customer performs a remote desktop session in TeamViewer it sometimes attempts to connect to an IP address rather than to a URL. When running a reverse DNS lookup on the IP we can see the correct TeamViewer domain (which is allowed by policy but the IP is blocked for being uncategorized).
I have special group of users allowed to access TeamViewer servers (for desktop sharing). Unfortunately a lot of TV servers are not categorized, as TV application access them with IP addresses not with names:
When a request comes in for an IP address, attempt an RDNS lookup against the IP to see if a domain is returned. If a domain is returned then we can apply the correct policy based on the RDNS result.