Hello Joe, 

Thank you for reaching out to the community. The Spam Filtering Log, logs all of the spam checks done. You can actually search by the delivery log session ID to find specific Spam Filtering details regarding that specific session. The reason that this log is blank is likely due to you having spam checks set to exceptions only. This will only log if there is an error in the program relating to Spam Checks. 

You can change this setting by going to the troubleshooting page then changing the logging level of Spam Checks. 

Please let me know if this answers your question!

Hoping to hear from you soon!

Kind Regards,