Best free email blacklist checkers compared
The best free blacklist checker depends on how wide you want to cast. To test an IP against the largest number of DNSBLs at once, MultiRBL (valli.org) queries hundreds of lists. For a plain-English read on a curated set of high-signal blocklists plus the next step to delist, Relaymetry checks the lists that actually affect delivery. The table below lays out five free tools side by side.
How these tools differ
All five tools check whether an IP or domain is on a blocklist, for free and without a login. The main difference is how many lists they query and what they do with a hit. MultiRBL (valli.org) and DNSBL.info query a very large number of DNSBLs, so they surface listings a smaller set would miss, at the cost of noise from lists few mailbox providers actually use. Spamhaus checks its own authoritative zones. HetrixTools and MXToolbox cover a broad standard set. Relaymetry checks a curated set of high-signal zones and, on a hit, links straight to the delisting page and explains what to do, rather than leaving you with a raw yes.
| Relaymetry | MXToolbox Blacklist | MultiRBL (valli.org) | DNSBL.info | HetrixTools | Spamhaus Reputation Check | |
|---|---|---|---|---|---|---|
| Checks IP and domain | Yes | Yes | Yes | No | Yes | Yes |
| Delisting guidance | Yes | Yes | No | Yes | No | Yes |
| No login | Yes | Yes | Yes | Yes | Yes | Yes |
| Public API | No | Yes | No | No | Yes | No |
| IPv6 support | No | No | Yes | No | Yes | Yes |
| Zones checked and catch | Curated high-signal zones; no login | Monitoring is paid; broad standard set | Many DNSBLs incl. IPv6 | Large IP-focused set; removal links | Free tier limited; monitoring paid | Own zones only; API needs a key |
Related comparisons
Common questions
Which free blacklist checker covers the most lists?
MultiRBL (valli.org) and DNSBL.info query the largest number of DNSBLs, so they are the tools to reach for when you want maximum coverage. The catch is that many of those lists carry little weight with major mailbox providers, so a hit on an obscure list is not always worth acting on. A curated checker like Relaymetry focuses on the zones that actually influence delivery and tells you what to do about a listing.
My IP is on a blacklist. What do I do?
First confirm the listing on the blocklist operator's own site, since checkers can cache. Then follow that operator's delisting process, which usually means fixing the root cause (an open relay, a compromised account, or a bad sending pattern) before you request removal. If your mail is landing in spam more broadly, our guide on why emails go to spam covers the common causes.
Do these tools check IPv6 and domain blocklists?
It varies. Most cover IPv4 well; IPv6 and domain (URI) blocklist coverage is less consistent, which the table marks per tool. If you send over IPv6, confirm the checker actually queries IPv6 zones rather than silently checking only the IPv4 address.