I have several clients who are having the same problem. If you look in Exchange System Manager (both in 2000 and 2003), under smtp current connections, there are a number of domains/ip addresses that seem to stay connected for an extended period of time. Some for 10-20 minutes, which can slow the server down considerably. If I disconnect them manually, they seem to just pop back upeither with the same address, or a different one. Is there a way to have Exchange (or another service) to automatically reject smtp connections that are coming from a known blacklisted source? Or even if they do not contain a reverse lookup.