autowhitelist_captcha http://wiki.qpsmtpd.org/plugins:spam:autowhitelist_captcha
This plug-in is a whitelist which automatically maintains itself based on well known and widely used Captcha authentication where a user must identify characters within an image. You can define one ore more mail- domains or single email-addresses that will be protected by this auto- whitelist plugin. If the sender of an email is not whitelisted, he will get an automatic reply-mail which includes a Captcha image which he can solve in his answer-mail. If the Captcha-string is correct, he will be automatically added to the whitelist, otherwise he gets a new Captcha via email until he succeed or failed for 5 times (then he will be blacklisted). Use this plug-in to efficiently protect your emails against Spam, because Spam-senders will never receive the Captcha mail (because they use faked email addresses) or if they do, they will never answer it. Your business contacts, friends and family will solve the Captcha because it's easy and they really want to get in contact with you. If you add all of your friends emails to the whitelist up-front, they will never need to solve the Captcha anyway. I recommend to download the plug-in from one of the CPAN mirrors: http://search.cpan.org/~mpelzer/ The archive contains not only the plug-in, but also the config-file and some nice MIME email-templates in german and english! It will take some time until the archive will appear on the mirrors.
