blacklist check

Overview

a DNS blocklist (DNSBL), also called a real-time blocklist (RBL), is a published list of IP addresses that have sent spam or shown abusive behaviour. receiving mail servers query these lists in real time: when your server connects to deliver a message, the receiver reverses your IP, appends the list's zone (e.g. 4.3.2.1.bl.spamcop.net) and does a DNS lookup. an answer in 127.0.0.0/8 means "listed" — and the message is rejected or filed as spam. that is why one blocklist entry on your sending IP can quietly tank deliverability while everything on your side looks fine. this tool resolves the IPs behind your domain — the A record (your website) and the A records of your MX hosts (your mail servers) — and queries each against six blocklists that reliably answer over Cloudflare's public DNS. it reports, per IP and per list, whether the IP is listed, clean, or unavailable. one gap: Spamhaus, the most widely used blocklist, refuses queries from public resolvers and returns a block sentinel instead of a real answer, so it is not included here — treat a clean result as "clean on these six lists", not "clean on Spamhaus".

How to use

1. enter a domain — we resolve its A record and its MX hosts to IP addresses.
2. read the per-IP results — each web and mail IP is checked against all six lists; a red dot means that list flags it.
3. act on any listing — a listed MAIL IP is what hurts email — follow that list's delisting process (see References).
4. run the full scan — blocklisting is one signal; the full dossier also checks SPF, DKIM, DMARC and TLS, which is what actually decides inbox placement.

Examples

input
example.com

output
1 IP checked (web) · not listed on any of the 6 blocklists

input
domain whose mail IP was compromised

output
mail IP 203.0.113.9 · listed on Barracuda (127.0.0.2), SpamCop (127.0.0.2) · clean on the rest

Common mistakes

• check the sending IP, not just the web IP — deliverability depends on the IP your mail LEAVES from. if you send via Google/Microsoft/a relay, your MX (inbound) IP is not your sending IP — check the sending host directly.
• shared hosting = shared reputation — on shared hosting your IP's reputation is the sum of every tenant. a neighbour's spam can list an IP you don't control.
• Spamhaus is not checked here — Spamhaus blocks public resolvers, so this tool can't query it without a Data Query Service key. clean here does not mean clean on Spamhaus.
• delisting takes time — most lists auto-expire entries in days to weeks once the abuse stops. fix the cause first or you'll be relisted.
• UCEPROTECT levels 2 and 3 list whole networks — level 1 is per-IP; the higher levels list entire ASNs and are widely ignored. we check level 1 only.

FAQ

Related tools

• dmarc checker — find and parse a domain's DMARC policy record at _dmarc.<domain>.
• spf checker — find and parse a domain's SPF (sender policy framework) record.
• mx lookup — list the mail exchangers (MX records) a domain advertises, sorted by priority.
• dkim lookup — probe common DKIM selectors (default, google, k1, selector1/2, mxvault) for a domain.

References

1. Barracuda Reputation Block List
2. SpamCop Blocking List
3. Spamhaus DNSBL usage
4. UCEPROTECT Network