The base fee doesn't need to be monthly, they can take $50 dollars as a one time registration verification fee. That should be enough to cover their compute costs for the year, specially when you pool in that from multiple customers. Who is spamming with 100 monthly emails? How much compute do they need to verify you aren't spamming. They can bake all of that into the pay per use price, they choose not to and I'm glad cloudflare is offering this.