Clearly how end-users define spam varies in a very extreme way.

You are servicing several domains on your Netcleanse server.  End-users on most of the domains are happy with the global configuration settings but several other domains have issues with false positives and false negatives.

You can build per domain settings using the PROFILE feature and set configuration to please each domain individually.  

Instead of trying to please multiple domains with one global configuration, build them their own configuration and let them manage it.

Durable, simple to set up, Profiles allow you to leave the administration of things like black and white lists and spam thresholds to your clients.