This is what proof of work should have been used for, invented long before Bitcoin. But it seems to never have caught on. Purelymail uses the system to protect

This is what proof of work should have been used for, invented long before Bitcoin. But it seems to never have caught on. Purelymail uses the system to protect itself from spam: https://purelymail.com https://purelymail.com Wikipedia links: https://en.wikipedia.org/wiki/Proof_of_work https://en.wikipedia.org/wiki/Proof_of_work https://en.wikipedia.org/wiki/Hashcash https://en.wikipedia.org/wiki/Hashcash