I think you are misunderstanding the way that penny black works, the mail won't be delivered unless the logic problem is solved. It doesn't matter what OS the sending computer is using, the logic problem will still need to be solved.
The CPU usage system was initially proposed by people outside of Microsoft. (read the penny black link in the article for details)
rchandra Stargate Universe fan Premium join:2000-11-09 14225-2105
I saw a proposed implementation of this while watching the 2004 (anti-)spam conference at MIT. It doesn't seem like this is practical. Moore's law of computing power is one problem (sort of), mailing lists is another. Could you just imagine how long it would take to send out notifications of an available security patch? How many thousands or millions of recipients are there on the typical watch list like that? It would be time for the next OS release by the time the last recipient got the notice for the first update. -- English is a difficult enough language to interpret correctly when its rules are followed, let alone when a writer chooses not to follow those rules. Blog is here
The way I read the description of the system led me to believe that the end user can make a list of safe people to receive email from. The people on the safe list do not get a "here is a problem for you to solve" type response.
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