Blacklist / RBL Checker

Check an IP or domain against the blocklists and reputation databases that actually move mail.

Accepts IPv4 (1.2.3.4), IPv6, or a hostname like example.com.

How this blacklist checker works

A DNSBL is a public DNS zone listing IPs (an RBL) or hostnames (a DBL) that have shown up in spam, malware or abuse traffic. Receiving mail servers query the zone during SMTP. One match on the wrong list is enough to land your mail in junk or get it rejected at the gateway, usually without a useful bounce.

Type a domain or IP above and the checker resolves the sending surface (A, AAAA and the IPs behind each MX) then queries the lists that actually move mail in parallel. That includes Spamhaus ZEN, SBL, XBL and PBL, Spamhaus DBL, SURBL, Barracuda, SpamCop and the three UCEPROTECT levels, alongside a long tail of smaller zones. Every hit shows the return code, the listing category and a direct link to the provider's delisting form.

Which blocklists actually matter?

Spamhaus ZEN is the one Gmail, Microsoft and most enterprise filters consult on every inbound connection. Spamhaus DBL covers the From-domain and any URLs in the body. SpamCop feeds AOL, Yahoo and several appliance vendors. Barracuda and SORBS still drive a lot of enterprise gateways. UCEPROTECT levels 2 and 3 are aggressive and noisy, and most receivers ignore them, but a hit there usually means a neighbour on your /24 or your upstream AS is in trouble.

Our take: a Spamhaus ZEN or DBL hit is a delivery emergency. A UCEPROTECT-3 hit is an early warning. Treat them differently.

IP reputation or domain reputation?

Both, and they fail differently. IP listings (SBL, XBL, PBL, Barracuda) attach to the sending server. Domain listings (DBL, SURBL, URIBL) attach to your brand and the URLs you ship inside messages. Modern filters at Gmail and Microsoft weight domain reputation more heavily — senders rotate IPs all the time, but they rarely rotate brand domains. A clean IP with a domain on the DBL still lands in spam.

My brand-new IP is already listed. Why?

Two usual suspects. The previous tenant burned the reputation and the listings stayed attached to the address. Or the IP falls inside a residential or dynamic range that Spamhaus PBL lists by default — those ranges should never originate mail directly, only relay through the ISP's smart host. Check the PBL detail page for the specific reason.

What to do: for inherited reputation, warm up slowly — low volume to engaged recipients, ramped over two to four weeks. PBL listings won't lift until your ISP asks for removal.

Why this matters now

A listing on the wrong zone shows up as bounces within hours. Microsoft typically returns 550 5.7.1 when a reputation check fails. Gmail surfaces it as 421-4.7.0 with a Spamhaus reference. Most other receivers drop the mail into junk silently and you only find out when a sales rep notices their reply rate halved.

Many listings trace back to a broken FCrDNS setup on the sending host — the PTR doesn't round-trip, so the receiver downgrades the connection. The reverse DNS checker confirms whether yours does.

Where to go next

For policies and removal costs per provider (some charge, UCEPROTECT being the notorious one), see the RBL provider reference. If the listing is reputation-driven rather than abuse-driven, fix the authentication stack first: SPF, DKIM and DMARC all feed the score that put you on the list.

Frequently Asked Questions

Common questions about email blocklists and reputation-based filtering.

Fix the cause first, then request removal. Spamhaus, SpamCop and Barracuda each publish a self-service delisting form linked from their listing-detail page. Expect a 24 to 48 hour propagation window after approval.

Asking for delisting before you've actually fixed the underlying issue — an open relay, a compromised account, a marketing send that hit a spam trap — almost always lands you back on the list within a day, and on a longer cooldown. Read the listing reason. Fix that. Then click delist.

Mail bouncing because of a reputation hit at Microsoft usually returns 550 5.7.1. At Gmail it shows up as 421-4.7.0 with a Spamhaus reference in the text.

It depends on the list and on why you ended up there. Spamhaus XBL listings (compromised hosts) expire automatically within hours once the abuse stops. SBL listings (deliberate spam sources) need a manual delist. PBL listings (residential or dynamic ranges that shouldn't originate mail) are effectively permanent unless your ISP asks for removal. SpamCop drops the listing 24 hours after the last report.

Reputation systems are a different category. Microsoft SNDS and Google Postmaster Tools rebuild gradually over 7 to 30 days of clean sending. There is no manual reset and no support ticket that will speed it up.

Less than people think for the IP side. The outbound IPs belong to Google or Microsoft and their reputation absorbs the small share of bad senders on each shared address. You will almost never see an SBL listing against a Workspace-relayed message.

Domain reputation is the part you still own. A phishing URL inside a marketing send flags your From-domain on Spamhaus DBL or SURBL no matter who relayed it, and that listing follows you to whichever provider you switch to next. If you run a dedicated IP through Microsoft 365 High Volume Email or Google's high-volume sender programme, you also inherit reputation responsibility for that IP.