Problem
Event log messages show DNSBL query errors.
Solution
Log messages such as:
RblServer::check 20.4.90.202.zen.spamhaus.org error=2 : 'Host name lookup failure'
could mean that the query is being refused because it exceeds pre-defined service limitations by the DNSBL service provider. If you have very high volumes of email traffic, consider providing a DNSBL server on your local network by synchronizing the DNSBL database to it. For details, consult your service provider.