Martel, You are correct that I did not look into the details and I have not tried the software. I'm also very unlikely to try it for a few reasons:

I understand that it allows a spam-free like channel between friends who are all using UseBestMail but I still don't get the point really. I'm not likely to get any spam from my friends/colleagues/business associates and their email is extremely unlikely to be tagged as spam by SimpleFilter. Your basic principal "to stop spam before it is sent" really breaks because a spammer certainly isn't going to use UseBestMail.

I understand the whitelisting component. Just about any spam technique uses whitelist/blacklist type features. We typically don't require them for SimpleFilter except for the odd newsletter here and there that look very much like spam.

I'm not a fan of challenge/response at all. I am annoyed when I receive a challenge and more times than not I'm unlikely to actually bother dealing with a challenge unless the email is important. Just recently I tried sending an email to a friend and received a challenge. It was just a quick one line email about something unimportant. You guessed it, I couldn't be bothered dealing with the challenge. I suppose I will at some point if I need to get an important email through.

Under your point of "receipt of mail from strangers" it sounds as though one is likely to wade through all the spam picking out the 1 or 2 that might be legit. I don't have time for that and frankly don't need to do that with SimpleFilter. I check less than 10 emails out of hundreds a day that end up in my spam folder that could potentially be a legitimate email. I realize that this is a user decision on whether to ignore these messages and potentially false positives but with SimpleFilter and tagging of Low, Medium, and High we've found that Medium and High can essentially be ignored without worrying about false positives at all. In fact most of our corporate customers drop Medium and High at the server level shortly after running SimpleFilter for a few weeks.

In any event, I do like to see you fighting the battle from a different angle. If we hit the spammers from every possible angle maybe one day we will win this fight entirely. For the time being SimpleFilter has made SPAM a non-issue for me in dealing with my email inbox. Tim