If you acknowledge it, you have automatically told him he has a valid email address for another person he can continue to send junk to. That means more junk email, and hope he doesn't sell it to some list somewhere. Anyone that answered him, (some emails can auto detect being opened as well) has already confirmed their email address to him.... so you can create a rule that deletes emails that come from him in Outlook as Gary suggested.

Brian, stage 4 oral cancer survivor. OCF Founder and Director. The first responsibility of a leader is to define reality. The last is to say thank you. In between, the leader is a servant.