Enter a domain or IPv4 address to check it against major DNS blocklists and see any listing return codes.
This checker queries public DNS blocklists using DNS-over-HTTPS. For an IPv4 address it checks the address, with its octets reversed, against zen.spamhaus.org, bl.spamcop.net, b.barracudacentral.org and dnsbl.sorbs.net. For a domain it checks the domain form against dbl.spamhaus.org and multi.surbl.org. A list answers with an A record in the 127.0.0.x range when the entry is listed (the last octet is the list's return code) and with NXDOMAIN when it is not. Important limitation: some lists, notably Spamhaus, restrict the answers they give to queries that arrive through public resolvers, so a result here is indicative, not definitive, confirm any important result on the list operator's own lookup page before acting on it.
What does a 127.0.0.x answer mean? DNS blocklists signal a listing by returning a loopback address instead of NXDOMAIN. The final octet is a return code whose meaning is defined by that list, for example, different codes can distinguish a spam source from an exploited host, so check the code on the list's own documentation.
Why might a result here differ from the list's own site? Some list operators limit or refuse answers to queries coming through large public resolvers, to manage volume and require direct lookups. When that happens this checker can show not listed or inconclusive while the operator's own lookup shows a listing, which is why results are described as indicative.
If an address is listed, what should be done? Find out why from the list operator's lookup page, fix the cause (for example a compromised account or an open relay), and then follow that list's removal process. Removal procedures and times differ by list, and some listings expire on their own.