Route-based protection against large-scale message floods (spam, mail bombs, etc.). “The war won’t be over until the last spammer’s head is stuck onto a spear at the city limits.” — Paul Vixie, NANOG mailing list, Sept.1997.
You can download it from the following link: https://packetstormsecurity.com/files/download/13350/spamshield-1.40.tar.gz
Source: https://packetstormsecurity.com/files/13350/spamshield-1.40.tar.gz.html