I haven’t been enthusiastic about challenge-response spam blocking because I think that it’s an unreasonable burden to put on strangers and friends of friends who want to do talk to me but don’t plan to sell me something. This is also a major annoyance to strangers who reply to a message I sent them. Others have raised the concern that the challenges Mailblocks generate look a lot like spam themselves.

But my current spam filters have been failing lately because a lot more spam is personally addressed to me. So, I wrote filter that looks up the sender and if they’re not in my address book it flags them as “spam?” and moves them to a folder where I can check them out later.

It seems to work pretty well, and it keeps the burden off spam enforcement off my correspondents, where it never belonged. I’m not saying it’s sufficient. It’s just a better solution to the specific problem addressed by challenge-response.

Here’s my stupid question: If this is a better, cheaper (free), unpatentable, and far-simpler solution than challenge-response spam filters, is challenge-response a business at all?