Blocklist sources and terms
Which DNS blocklists the blacklist checker queries, why, and which ones it deliberately leaves out.
We only query lists whose operators publish terms that allow a free public lookup website to use them. Terms were last reviewed on ; operators can change them at any time, so follow the links for the current version. Queries go through our server's own DNS resolver, not through public resolvers, and each list is sanity-checked hourly with its RFC 5782 test addresses: a list that claims the address 127.0.0.1 itself is listed is treated as broken and its answers are ignored.
Lists in use
| List | What it lists | Terms (summary) | Status |
|---|---|---|---|
| DroneBLdnsbl.dronebl.org | IPs of abusable or compromised hosts: open proxies, botnet drones, brute-force sources. | Free of charge for commercial and non-commercial use. Terms | Enabled |
| 0spambl.0spam.org | IPs observed sending spam to 0spam traps. IPv4 only. | Stated as free for all uses, including commercial. Terms | Enabled |
| PSBL (Passive Spam Block List)psbl.surriel.com | IPs that sent mail to spam traps and are not known legitimate mail servers. IPv4 only. | "Anybody is free to use PSBL." Terms | Enabled |
| Mailspike Blacklistbl.mailspike.net | IPs with poor sending reputation based on Mailspike's traffic data. IPv4 only. | Free up to 100,000 queries per day. Terms | Enabled |
| s5h.net RBLall.s5h.net | IPs seen sending spam or attacking s5h.net traps. IPv4 only. | Stated as free of charge, currently without limit. Terms | Enabled |
| Spamhaus ZEN (via DQS)zen.dq.spamhaus.net | Combined SBL, CSS, XBL and PBL: spam sources, compromised hosts and end-user IP ranges. | Requires a Data Query Service key. The free key is for non-commercial use only; a public or ad-supported site needs a paid licence. Public mirrors refuse queries from shared hosting and public resolvers. Terms | Off — needs DQS key / commercial licence |
| Abusix Mail Intelligencecombined.mail.abusix.zone | Combined IP blocklists (spam sources, exploited hosts, dynamic ranges). | Requires an API key. The free tier (5,000 queries/day) is intended for smaller businesses and non-profits; confirm eligibility with Abusix. Terms | Off — needs API key |
| SpamRATSall.spamrats.com | IPs with missing reverse DNS, dynamic-looking names, spam or authentication abuse. IPv4 only. | Requires a free API key; the free tier is non-commercial only (max 40,000/day). Commercial use is paid. Terms | Off — needs API key / commercial licence |
| Barracuda Reputation Block Listb.barracudacentral.org | IPs with poor sending reputation. IPv4 only. | Requires registering the querying DNS server's IP address with Barracuda. Terms | Off — needs Registration |
Lists marked "Off" require an API key, registration or a commercial licence. The site operator can enable them in the configuration after obtaining permission.
Lists not used
- SURBL — Any product or service using its data requires a paid usage agreement. Source
- URIBL — Free mirrors are for low-volume end users; other use needs the paid data feed. Source
- Spamhaus DBL (domain list) — Same licensing as Spamhaus ZEN (see above). Source
- Invaluement — Paid subscription only. Source
- SpamCop, UCEPROTECT, Backscatterer, Blocklist.de, JustSpam, GBUdb, Suomispam — We could not find terms that clearly permit use by a public lookup website. Off until the operators confirm.
- SORBS — Shut down in June 2024.
- NiX Spam — Shut down in March 2025; its zone now reports every address as listed.
- WPBL — Shut down in 2023.
What a listing means
A blocklist entry records that an operator saw something from that address they consider abusive, or that the address is in a range they block by policy (for example home internet connections). It is not proof of malicious activity by the current owner of the address. If you believe a listing is wrong, contact the list operator through its removal page.