A patch for the tcpserver rblsmtpd, which transforms it into greysmtpd. Greylists IP subnets (ip/24). It uses a directory/file structure to decide if the IP net should be greylisted or not which makes it extremely fast. At most 3 stats is used to decide when to let through or greylist.
This patch has been discontinued since it doesn’t work very well anymore. Nowadays I use postfix-policyd which has support for honeypot addresses, black/white listing of IP’s/ranges and “real” greylisting. The downside of it is the usage of a MySQL database and therefore resources such as memory and cpu…