What is an IP blacklist?
A DNS blocklist (DNSBL), often called an RBL or blacklist, is a public database of IP addresses that have sent spam, hosted malware or shown other abusive behaviour. Mail servers query these lists for every incoming connection, and many firewalls and forums use them too. If your mail server's IP is listed, your emails may bounce with errors like 554 5.7.1 Service unavailable; client host blocked or quietly land in spam.
How the check works
To check 203.0.113.25 against a list such as bl.spamcop.net, we look up the DNS name 25.113.0.203.bl.spamcop.net. If the list returns an address in 127.0.0.0/8, the IP is listed, and many lists also publish a TXT record with the reason. If the name does not exist, the IP is clean. We run all the queries in parallel and show which lists answered.
Why does my IP keep getting blacklisted?
- A compromised device on your network is sending spam or is part of a botnet.
- An insecure mail server or contact form is being abused as a relay.
- Missing or generic reverse DNS (PTR) on a mail server makes it look like a home connection.
- Shared hosting or shared IPs: another customer on the same address misbehaved.
- Dynamic residential ranges are listed by policy on some lists, because they should not send mail directly.
How to get delisted
- Find and fix the cause: scan devices, secure the mail server, rotate leaked passwords and stop any bulk sending.
- Make sure the server has valid reverse DNS and that your domain has SPF, DKIM and DMARC.
- Use each list's removal link above. Some, like SpamCop, expire listings automatically once the spam stops.
More detail in IP blacklisted? How to check and get delisted.
Frequently asked questions
Why is Spamhaus not in the results?
Spamhaus blocks queries that arrive through large public DNS resolvers, so any answer we received would be unreliable. Use Spamhaus's own lookup page for an accurate result.
Does a listing on one small list matter?
It depends on who uses the list. Major lists affect deliverability widely; smaller lists may be used by only a few servers.
Can I check IPv6 addresses?
Very few blocklists publish IPv6 data, so this tool checks IPv4 addresses only.