IP Blacklist Checker

Frequently asked questions

What is an IP blacklist (DNSBL)?

A DNS blocklist is a list of IP addresses reported for sending spam or hosting abuse. Mail servers look up the sender's IP in these lists, using a DNS query, and may reject or flag the message if it is listed. Each list has its own rules for adding and removing addresses.

How does this checker work?

It reverses the octets of the IP address, adds each list's domain name, and asks DNS whether that name exists. An answer in 127.0.0.0/8 means listed. No answer means not listed. This is how mail servers do the same check.

Why is my IP blacklisted?

Common causes are a hacked account or website sending spam, a compromised device on your network, a sending IP with no reverse DNS record, or sharing an IP with a spammer on a shared host. Some lists, like the Spamhaus PBL, simply list dynamic home IP ranges that should send mail through a provider instead.

How do I get delisted?

First stop the cause: scan for malware, secure compromised accounts, and fix reverse DNS and SPF. Then use the removal form of each list that names you. Many lists drop an address by themselves after a few days of clean behavior. Requesting removal before fixing the cause usually gets you listed again.

Does being on one list mean my email will be blocked?

Not always. Each receiver chooses which lists it uses and how much weight to give them. Spamhaus and Barracuda listings matter the most because they are widely used. A single listing on a small list often has little effect.

What does "could not check" mean?

The list did not give a usable answer: it timed out, or it refused the query. Spamhaus, for example, blocks queries from some large public DNS resolvers. These results are never counted as listed or clean. Run the check again if you need a complete result.

Why is Spamhaus not included?

Spamhaus refuses queries sent through public DNS services, including the one our checker has to use, and answers them with an error code instead of a result. Reporting that as clean would be wrong, so Spamhaus is left out. Check it directly on the Spamhaus website. SpamRats is left out for the same reason.

Why is only IPv4 supported?

Almost all public blocklists are keyed by IPv4 address. Entering a domain checks the first IPv4 address it resolves to.