[austenallred]

That's basically what Craigslist does when it "ghosts" content. It tells you it published it, and you can even see it when you follow the direct link, but it doesn't appare on the listings. Eventually CL spammers started checking the actual listings.

I assume the same thing would happen with email; spammers would use a few of their own email addresses on the list to make sure the emails are actually being delivered. It would be a pain for a while for sure.

[ma2rten]

HackerNews does the same when it hellbans people. Let's just say it works for some kind of spammers (the less professional ones).