I had this exact same idea about a week ago! You can create a forwarding email address that has a payment barrier to sent emails through. Regarding point numbe

I had this exact same idea about a week ago! You can create a forwarding email address that has a payment barrier to sent emails through. Regarding point number 3, I think the service should charge a small fixed fee for each accepted email not some percent. This would enable users to create services based upon email alone. You could charge people for support or consulting with your entire operation occurring over email.