Question 1

What is an IP blocklist (RBL)?

Accepted Answer

A blocklist, or real-time blackhole list (RBL), is a DNS zone that lists IP addresses known to send spam. Mail receivers query these lists and reject or mark as spam any mail coming from a listed IP. Being on one is one of the fastest ways to lose deliverability.

Question 2

Which blocklists does this checker test?

Accepted Answer

It queries 9 widely used DNS blocklists: Spamhaus SBL, PBL and XBL, SpamCop, Barracuda, CBL, UCEPROTECT Level 1 and Level 2, and SORBS. These are among the lists most major mail providers consult.

Question 3

My IP is on a blocklist. What do I do?

Accepted Answer

First confirm the listing is not a false positive. If it is legitimate, request delisting through the blocklist operator (for example check.spamhaus.org) and fix the underlying issue, such as an open relay, compromised account, or a shared IP with a spammer. If you cannot delist quickly, move sending to a clean IP or a reputable email service provider.

Question 4

Is being on a blocklist the same as being blacklisted by Gmail?

Accepted Answer

No. Blocklists are third-party reputation lists. Gmail and Microsoft maintain their own internal reputation systems on top of them. A clean blocklist result is necessary but not sufficient for good deliverability, SPF, DKIM and DMARC also matter.

Question 5

Is this blocklist checker free?

Accepted Answer

Yes. The IP blocklist lookup is free and requires no signup. You can optionally add an email to run and save the full deliverability audit, which adds SPF, DKIM, DMARC, TLS, reverse DNS and blocklist checks.

IP blocklist checker

Check the whole domain, not just the IP

Blocklists are only one signal