Active Spam Killer
Active Spam Killer (ASK) is a challenge/response system that encrypts information in MD5 fields within the message’s Subject: line. A sender who is not already whitelisted goes through a short confirmation process. The mail system of the recipient of the original message sends a challenge to the sender. The sender of the original message simply replies to the challenge, and the subsequent message is processed by the recipient’s email system. The MD5 header is analyzed, and the message is released from the holding area and is delivered to the recipient.
To install ASK, start by downloading the distribution from the Sourceforge repository, http://prdownloads.sourceforge.net/a-s-k/ask-2.4.1.tar.gz?download, into ...