Only spam free for you, perhaps. However that is as I and others have pointed out, an idea that thrives on inconveniencing other, innocent parties in an effort to make your mailbox spamfree.

As for millions of spammers, there's no way CR is going to scale to millions of mailboxes.

If you have the patience to plow through about 35 pages of text, please try http://www.oecd.org/dataoecd/5/47/34935342.pdf - it might help. And saves me trying to summarize that lot in a followup to a blog post.