DNS blacklists help you to determine whether message senders may be spammers or hackers. You can also report spam and suspicious addresses to a DNSBL for the benefit of others on the Internet. The larger blacklists contain millions of entries.
To use the DNSBL services listed below, type an IP address into the form they provide to look it up in the database. If researching the origin of a spam email, you can obtain its IP address from the mail headers (see: How To Find the IP Address of an Email Sender)private IP addresses used on local networks.