In theory, the idea is great. Anyone not in my addressbook who sends me an email is challenged for a response; if the response is received the email comes through. Ilesa claims this will eliminate spam; I argue it will only work until spammers figure out ways to make sure their email gets through.

But worse: SpamSlam only adds to the spam problem, instead of getting rid of it. Every spam message gets challenged (spam). Many of these challenges will bounce (more spam). Many non-spam messages will get challenged (still more spam). Spammers will know that you're alive since you've challenged them; in fact, you've challenged them to send even more spam. Aahhrgh! Floods of spam!

Furthermore, this method requires serious effort of both me and the email sender. Me, because I need to make sure my whitelist is up-to-date, so I do need to do some serious setting up (any integration with Address Book yet?). The receiver because (s)he is challenged. I can imagine people not willing to respond to the challenges sent to them. I for one would be very reluctant to do so. And then there are the mailing list problems and unsolicited-yet-wanted email problems, as pointed out by previous reviewers.

This product fights spam with spam. Other spam fighting efforts (such as adding Habeas headers or just bouncing spam) fail for the same reasons: too much hassle, or spam generators themselves.

I say the only way to get rid of spam is (1) keep your mail address as confidential as humanly possible and (2) delete spam by intelligent or fuzzy filtering. Apple's own Mail.app does a pretty good job. It's setup requirements are next to nothing and it's effectiveness somewhere in the high nineties.