I'm wondering the same thing. I recently setup the antispam filter on an Exchange 2010. It appears to be working, showing the number of emails that were marked as spam and the total scanned. However, when I click the shield log button, the log is blank. Is there something else I need to do to turn on logging or something? Is there another place the logs are stored? I'm primarily wanting to look for false positives to add the whitelist.