The Barracuda Reputation Block List (BRBL) is based on Barracudas system and operates collaboratively to fight spam. The automated spam trap, collection and rating system automatically adds IP addresses to the list when spam is detected.
Listing happens on an IP level and pretty low impactful to delivery. However if traffic is concentrated more B2B you have a higher chance of having delivery impacted.
Reason for listing
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).
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.
Barracuda allows direct removal requests to be made on site. Be sure to review your traffic prior to removal request to prevent your IP from getting blocked again.