The Barracuda Reputation Block List (BRBL) is based on the Barracuda Reputation System and operates collaboratively to fight spam. The BRBL provides a list of IP addresses which are sending spam. The Barracuda Reputation system uses automated collection methods to add and delete IP addresses from the BRBL.
The automated spam trap, collection and rating system automatically adds IP addresses to the list when spam is detected. Barracuda Networks does not manually add addresses to this IP list.
When email is received, the connection is automatically analyzed to determine if the connecting machine is either an open proxy or a node in a spam-generating botnet. If either is true, the IP address is immediately added to the Barracuda Reputation Block List (BRBL). The BRBL only lists single IP addresses.
Most IP addresses are listed as a result of directly sending spam or viruses to the Barracuda Reputation System's detectors. The Barracuda Reputation System detects spam by using honeypots, special addresses created to receive only spam and do not belong to any real user and through analysis of captive spyware protocol activity. In addition, the BRBL leverages some data derived from the Barracuda Blocklist (BBL) that is delivered to Barracuda Spam Firewalls as part of Barracuda Networks' product offerings.
Users that place multiple computers behind a NAT gateway/firewall system should block all outgoing port 25 traffic from all computers which have not been explicitly configured and maintained specifically as email servers. A single infected machine sending spam out through a network utilizing NAT can result in blocked email from the whole LAN.