The DNS IP BLACKLIST
The inps.de-DNSBL exists since 2007-12-29. It is queryable free of charge via the Domain Name System and can be used in conjunction with other DNSBL’s for a better spam filtering.
This blacklist contains IP addresses from which they have received mails, that were classified as spam. Your IP can be listed in this blacklist even if you have sent them a single SPAM message. IP addresses are kept in this list until the owner requests a removal. Email server admins can submit IPs to this blacklist via their API if they receive more than 250 SPAM messages daily.