DNS blocklists
About 28 live DNS blocklists — Spamhaus, SpamCop, Barracuda, DroneBL and more — mostly about spam, open proxies and infected machines.
- DNS blocklists
What it is
A DNS blocklist (DNSBL) is queried over DNS: reverse the digits of the address, add the list’s zone name and see whether it resolves. An answer means “listed”, and the answer code says why.
Mail servers use these lists to reject spam. We query about 28 of them live, a few at a time.
What it checks
- Spam sources (Spamhaus ZEN, SpamCop, Barracuda, UCEPROTECT and others)
- Open proxies and drones (DroneBL)
- Abuse and attack reports (blocklist.de, InterServer)
How to read the result
- Clean
- The list does not know the address.
- Listed
- The address is on the list. The reason (spam source, open proxy, exploited machine) is shown next to it.
- Blocked / unavailable
- The list refused the query or has a limit. This is not a verdict about the address.
Limits
- A listing on a policy list (Spamhaus PBL) only says the address is an end-user connection that should not send mail directly. We do not count it as abuse.
- IPv4 only.
- Lists differ a lot in strictness; one listing on a strict list matters less than several on different ones.
How it is used here
All lists are shown at once, listed ones first. Each listing adds points to the overall risk.