Check whether a sending IP or domain is on the blocklists that matter.

A listing on a major DNSBL can quietly stall a sending IP. This checker queries the widely used blocklists directly over DNS and reports each list's answer, including when a list could not be checked.

How it works

  • For an IP, the reversed address is queried against each DNSBL zone over public DNS.
  • For a domain, its IPv4 A records are resolved first (capped at 4) and each IP is checked.
  • Lists are tiered by weight — Spamhaus ZEN and Barracuda carry more signal than supplementary lists — and a failed query is shown as unknown, never as clean.

When to use it

  • Before pointing prospect traffic at a newly assigned sending IP.
  • When bounces or deferrals mention blocklists or reputation.
  • As a periodic spot-check on IPs behind active cold email sending.

Common failure cases

  • Treating a clean DNSBL result as proof mail will land in the inbox.
  • Ignoring tier-3 listings entirely — they carry less weight but can indicate an emerging problem.
  • Requesting delisting before fixing the behavior that caused the listing, which leads to relisting.

Examples

What good and bad signals look like

Clean result

0 listings across all checked lists

No checked DNSBL currently lists the IP. This is one reputation input, not placement proof.

Tier-1 listing

Spamhaus ZEN returns 127.0.0.4

The return code identifies the sub-list. Pause sending from that IP and follow the list's delisting process.

What to do next

  • For a listed IP: stop sending from it, identify the cause, then follow the DNSBL's delisting process.
  • Check the domain's auth records — reputation problems compound with missing SPF or DMARC.
  • GTM Inboxes monitors managed sending IPs against these lists continuously and can rotate a listed IP.
Stop babysitting IP reputation

GTM Inboxes monitors managed sending IPs against these blocklists automatically.

Related tools and workflows

Cold email domain checker

Check domain age and auth records alongside IP reputation.

DNS & auth checker

Verify SPF, DKIM, DMARC, and MX for the sending domain.

Managed SMTP infrastructure

Managed IPs include continuous blacklist monitoring and rotation workflows.

Cold email inbox calculator

Turn a DNS or authentication check into a conservative inbox-capacity plan.

FAQ

Does a clean blacklist result mean my email will reach the inbox?

No. DNSBL status is one reputation input among many. Placement depends on authentication, content, recipient behavior, provider filtering, and sending history.

Why does a list show as unknown instead of clean?

The DNS query to that blocklist failed or timed out. Reporting it as clean would be misleading, so the tool marks it unknown — retry shortly.