We see a significant amount of spam coming from senders who's originating server IP address does not have a reverse DNS entry.
The header will show similar to: "Received: from [46.150.229.158] (Unknown_Domain [46.150.229.158])by". Can we assume that legitimate email servers will all have a reverse DNS entry and therefore we should block all messages from an "Unknown_Domain"?
If so, how would we configure Brightmail to perform this action? We are running Brightmail Gateway 9.0.2-9.