Please check KB0011408 - Unblocking Your Email Server for a description of the Talos reputation service.

ITS maintains a small block list of hosts that pass DNS validation and have a good Talos reputation score, but still present problems. These hosts are not allowed to connect to our servers. Usually these are legitimate mail servers with technical problems, but hosts that are the source of spam, phishing, or other intentional attacks can also be placed on this list. Once the problems are corrected, the servers may be removed from the list.

System administrators whose servers have been blocked should contact postmaster@utexas.edu to resolve the problem. Requests must include the IP address(es) of affected server(s), and the date and approximate time (including time zone) of the most recent incident.