When a bad ip address list gets involved in spamming or other unwanted online activities, it may get flagged and land on one of these blacklists. These databases help ISPs and web servers block (or alert on) those IP addresses to protect them from malware, phishing and other bad activity. We can use a tool to check these lists and see if our own IP is on them.

Generally, smaller IP lists are safer to use as firewall blacklists as they have fewer unique IPs and a lower risk of false positives. However, they may not provide a full level of protection. Also, it is important to understand that these IP list providers only remove IPs when they are no longer considered problematic and not just when the list size gets too large. This is called their retention policy and can be seen in the chart above by paying attention to the column Their % and This %.

Building a Bad IP Address List for Enhanced Network Security

The most common cause of blacklisting an IP is due to a spamming incident. These incidents are detected by various antispam systems that then report them to the IP blacklists. The IPs stay in the blacklists for a pre-determined amount of time, unless they match the criteria again, and then they are removed from it.

The best way to prevent getting blacklisted is by ensuring that your email program is configured properly and that the virus scanner has up-to-date definitions. You can also limit access to your email server by implementing an authentication system that requires users to have a valid username and password to send or receive mail. If you still find yourself listed on an IP blacklist, you can try to resolve the problem by contacting the list owner and explaining the situation to them.