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What's a challenge and response spam filter?

Dave, perhaps you can enlighten me. I recently sent email to a colleague and got a message back telling me that if I wanted to have my message delivered, I had to click on a specific button indicating how many windmills were in a given picture. What's that all about?


Dave's Answer:

You've bumped into a challenge/response spam filtering system. The logic behind these is good: if you want to get a message to my inbox, prove to my little robot assistant that you're a human, not some insidious spam application trying to waste my time and resources.

How to do this easily? Well, you can't just send out a response message and ask for a reply, because that can be easily recognized and automatically answered, defeating the purpose of the spam filter in the first place. You could embed one of those weird "letters floating in space" decoding graphics and ask the user to figure out the response, but having an actual input form buried in an HTML message is too much hassle.

So how about a graphic that has a visual puzzle and a set of buttons that allow you to pick the correct answer?

That's exactly what MailFrontier does, among others, and it just so happens that I have a message from them in my own mailbox compliments of my colleague Brad Fallon. Here's what the graphic in the message looks like:

Mailfrontier spam challenge pic

Does this kind of system work? Yes, but. The problem is that lots of people -- myself included -- get too much email already and aren't willing to respond to challenge response systems. If your circle of colleagues and acquaintances are willing to jump through these hoops, then it might be a good solution for you, but if not, well, you'll be missing messages without ever knowing about it.


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Reader Comments To Date: 1

Judi said, on March 15, 2005 2:48 AM:

Yikes - I would hate to have to answer an email to send an email. Your mailbox would fill up fast! While it is a good idea, putting the burden of your spam filtering back in your correspondent's lap isn't the way to fix the problem in my opinion.

Starbucks coffee cup I do have a lot to say, and questions of my own for that matter, but first I'd like to say thank you, Dave, for all your helpful information by buying you a cup of coffee!

I do have a comment, now that you mention it!











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