IPv4 address blacklisting is done to control spam and prevent malicious activities. Every blacklist has its own set of criteria for blacklisting IP addresses of email spammers, which could be based on technical factors, ISP policy, and evidence-based. Technical blacklisting usually happens due to mail servers configuration issues, such as improper reverse DNS records and banner greetings, and mail servers operating within a range of suspicious IPv4 address blocks. ISP policy-based blacklisting is done when the receiving server decides not to accept emails from specific countries or ISPs, which are known for not following unsubscribe requests properly. Evidence-based blacklisting refers to those cases wherein the server has reliable proof to block an IPv4 address block because it has been involved[…]