challenge-response
Challenge/Response is a specific type of email filter. If you use a Challenge/Response (C/R) spam filter to protect yourself from spam, here’s what happens:Your email server or service receives a new inbound email message.The system checks to see if this is a person that you’ve talked to before.If yes, the mail is forwarded to you, skipping the challenge step.If no, the mail is NOT forwarded to you, and the sender receives a notification back — a “challenge.”The notification encourages the sender to “respond” to the “challenge” by clicking a link, solving a puzzle (think CAPTCHA) or (this is a new one I’ve seen recently) paying a designated charity.The charity angle might be new; but C/R has been around forever. I know well how it works, having built my own implementation of it back in the late 1990s. And I’ve been pointing out the imperfections behind the concept since all the