Email Blacklist Check

Email blacklist check

Is this mail server's IP blocklisted, and is its reverse DNS set up the way receivers expect?

How this check works

For each of 20 DNS blocklists, the check reverses the IP's octets and queries the list's zone; for 203.0.113.25 on SpamCop that's 25.113.0.203.bl.spamcop.net. An answer in 127.0.0.0/8 means listed, and the exact address is a return code that says why. We also fetch the list's TXT reason where one is published. All 20 lists are queried in parallel. The other lists are queried from your browser through Cloudflare's public DNS-over-HTTPS resolver. Spamhaus refuses queries that arrive through public resolvers, so it's queried from our server through its Data Query Service, which authenticates the lookup. If that service isn't available, Spamhaus is shown as "not checked" rather than guessed.

The same run checks reverse DNS: whether the IP has a PTR record, and whether that hostname resolves back to the IP (forward-confirmed reverse DNS). Gmail and many other receivers require both for sending IPs.

How to read the results

  • Listed (fail): the list returned a positive answer. How much it matters depends on the list: Spamhaus, Barracuda and SpamCop are widely used; others less so. The finding links to the list's removal process.
  • PBL (note): Spamhaus's Policy Block List marks ranges, such as home and mobile, that shouldn't send mail directly. It's not an accusation of spam. Send through your provider's authenticated relay instead.
  • No answer: the list timed out or refused the query. That isn't a listing. Some lists rate-limit or block certain resolvers.
  • N/A: the list doesn't publish IPv6 data, or the list isn't configured.
  • Reverse DNS: a missing or non-confirming PTR causes rejections at Gmail (4.7.23/5.7.25), even with a clean blocklist record.

What to do about a listing

  1. Find the cause before asking for removal: typically a compromised mailbox, an infected device sending on port 25, an abused web form, or poor list hygiene. Requesting removal without a fix leads to relisting.
  2. Request removal through the list's own page. Several lists expire listings automatically once abuse stops.
  3. Re-check here after the fix.

The full process is in How to get off an email blocklist.

Which IP should I check?

The IP that delivers your mail to the recipient's server. For hosted mail (Microsoft 365, Google Workspace, an ESP) that's the provider's IP, and the provider manages its reputation. Find the exact IP in a bounced or delivered message's Received: headers: it's the address in the topmost header added by the receiving server.

Updated 26 October 2026

Related checks

Guides for this check

FAQ

How do I get delisted?

First fix whatever caused the listing, such as a compromised account, open relay, or misconfigured server. Then visit the list's removal page linked in the results. Many lists also expire entries automatically after a period of clean behavior.

Why do some lists say IPv4 only?

Most blocklists only publish data for IPv4 addresses. For an IPv6 query, only lists that support IPv6 are checked, and the rest are reported as not checked rather than clean.

What does a "no answer" mean?

The list didn't answer: it timed out, refused the query, or the resolver couldn't reach it. It does not mean the IP is listed, and it does not mean the IP is clean.