Blacklist Check

DNS blacklists (DNSBLs or RBLs) are lists of IP addresses that receiving mail servers check before accepting email. If the IP your mail leaves from is listed, recipients may reject your messages or send them to spam — the bounce message usually names the list.

Why IPs get listed: spam sent from a compromised mailbox or an infected PC, an open relay or misconfigured mail server, missing reverse DNS (PTR), or simply sharing an IP with a spammer on cheap hosting. Check your mail server's or gateway's public IP — not a desktop's — and note that Microsoft 365 and Google Workspace send from their own IPs, which they manage.

Delisting: fix the cause first — reset compromised passwords, clean the infected machine, close the relay, set up PTR and SPF — or you'll just be listed again. SpamCop listings expire on their own once the spam reports stop; Barracuda takes removal requests on its Barracuda Central site.

Unavailable means that list couldn't be checked right now — it is not the same as clean. Spamhaus blocks lookups through public DNS like the one this site uses, so check Spamhaus directly on spamhaus.org.