One of a number of published lists of IP addresses that should be shunned for having broken some policy supported by the maintainer of the list. For example a number of lists contain the addresses of organizations that have sent or been involved in the sending of unsolicited bulk email. Network operators may decide to apply different rules to emails or other network traffic from addresses listed on RBLs whose policy they support, either rejecting them outright or subjecting them to greater scrutiny before transmitting them.