Based on statistics, the most abusive types of connections are those that either run dictionary attacks or mass mailings. They usually conform to the following four types: Botnet/Spammers from IP's with no Reverse DNS, Botnet/Spammers from infected PC's (Dynamic or Generic Reverse DNS), Email Marketing Companies and Compromised Servers
The use of IP Reputation is one of the most effective ways to reduce overhead, bandwidth, and of course Unwanted Bulk Email (UBE). The most common way to achieve this, is to check connections against IP Address lists and block them. Because we consistently receive large amount of spam information from ISPs, we are able to compile this data and use it in our anti-spam tools which we have made available to the public.
SpamRATS is dedicated to helping ensure that all forms of mail servers can choose to only accept messages from other properly configured mail servers. "Best Practices" dictates that mail servers should have correct Reverse DNS that reflects the operator of the mail servers.
We monitor this blacklist since 2015-01-01. More information: http://www.spamrats.com/