> Please look it over and try to poke holes in it, but I've worked pretty
> hard
> to make it as bulletproof as possible.
[..]
Whatever... any spam that *is* retried after the "block" is aged gets
through. Or have I got that wrong?
Lets say a spammers has gained control over a specific IP address for an X
amount of time. He normally sends out 1M messages via that IP. So now to
get around this block, he will send out 2M messages retrying delivery. This
increases his costs slightly but not to the point where it becomes
unprofitable. The reason why spammers have not tried this approach yet
become this blocking method has not been widespread.