Right now anti-spam is a big business, not much need for a prize.

In my plan all that’s needed is a large enough network of spare servers to act as these MXs that you can be sure at least one of the ones you use will be up, and the network has the capacity to handle the real mail. The machines are sharing via an internal channel the frequency counts of mail attempts from the billion untrusted IPs, and start to simply refuse connections for a while from IPs sending mail too fast, so their mail load can be managed. But it will still be large.

However, since speed is only a secondary consideration it’s something to easily run on spare servers, older servers, machines sitting around etc. You could also run one of your own if you like but generally you would just subscribe to somebody else’s. (You could also run one of your own on a 2nd IP address used by your own mail server, so no new hardware is needed, and just nice the process down low.)

The servers do delay mail by long enough to send and receive the regular updates on mail volumes over IP blocks. I haven’t designed a protocol for that but I think a fairly efficient one should be possible.

But again the key gain is the rest of the world doesn’t change their SMTP senders at all, not right away. Very little breaks because you install it (only large mailing list hosting on unknown sites.) Most other anti-spams tend to break things right away for large numbers of innocents, which makes them poor choices.