Is this IP on a spam blacklist?

What an IP blacklist check does

Email servers and websites often consult public blocklists to decide whether to trust an IP address. These lists are called DNSBLs, short for DNS-based blocklists. Each one is run by a different group and has its own rules for why an address is added: sending spam, being part of a botnet, running an open proxy, or sitting in a range that should not send mail at all.

This tool asks several free lists about an IPv4 address and shows you the answer from each, so you can see which lists, if any, include it. If you send email from a server and messages are being rejected, checking its address here is a sensible first step.

How the check works

A DNSBL lookup is an ordinary DNS question. The address is written backwards and added to the name of the list, and the list's answer tells us whether the address is on it. Our server asks every list at the same time, waits up to three seconds for each, and shows the result. The lists we ask are Spamhaus ZEN, SpamCop, Barracuda, PSBL, UCEPROTECT level 1, DroneBL and s5h.net.

Results are kept for one hour, so asking again straight away shows the same answer. To keep the free lists available, the tool allows 10 checks a minute and 50 a day for each visitor.

When a list says "not checked"

Some lists refuse queries they cannot attribute properly. Spamhaus, for example, blocks queries that arrive through large public DNS resolvers, and answers with a special code instead of a real result. We use our own server's resolver, but if a list returns an error code or does not answer within three seconds, we show "not checked" rather than guess. Not checked does not mean the address is clean.

If an address is listed

• Open the list's own lookup page, linked next to each result, to see the reason and the date.
• Fix the cause first. Removal requests usually fail, or the address is listed again, if the underlying problem such as an infected machine or an open mail relay is still there.
• Follow the list operator's removal process. Some lists remove entries automatically after a period without bad behaviour; others require a request. Never pay a third party to do this for you.
• Remember that shared hosting and mobile addresses are often listed because of other customers.

Limits

This tool checks IPv4 only for now. A clean result on these lists does not mean other lists, or mail providers' own reputation systems, will accept the address. Private and reserved addresses cannot be checked.