The IP Block List Providers feature of the Anti-spam agents in Exchange 2007 is a valuable tool to cut down on spam from known senders. The sucess of the feature depends on the block list providers that you use so how can you determine if they are actually catching spam? Just open up the Exchange Management Shell and navigate to the scripts folder within your Exchange Server install (e.g. C:\Program Files\Microsoft\Exchange Server\Scripts\). Then type in Get-AntispamTopRBLProviders.ps1 and hit Enter.
It can take a while to process but once completed you will see a list of each block list provider and the number of messages it blocked.
To fine tune the results you can use the -StartDate and -EndDate parameters.