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Reverse DNS / rDNS
Blacklist Check
50+ DNSBL blacklists
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IP address details
Blacklist check
Instantly check whether your IP address or domain is listed in 50+ major DNS blacklists (DNSBLs). Spamhaus, Barracuda, SORBS, SpamCop and more on a single screen.
About DNSBLs
DNSBL (DNS-based Blackhole List) or RBL (Realtime Blackhole List) are lists that publish IPs and domains known to send spam. Mail servers query these lists via DNS for incoming connections; if there is a match, the email may be rejected or marked as spam.
The query method is simple: the IP's octets are reversed and the list's domain is appended (e.g. for 1.2.3.4 the Spamhaus ZEN query is 4.3.2.1.zen.spamhaus.org). If the returned A record is in 127.0.0.x range, the IP is listed.
This tool uses Cloudflare DNS-over-HTTPS in your browser. Some lists (like Spamhaus) may reject queries coming from public DNS resolvers under heavy load; results are informational — verify with your own resolver in production.
Reasons for Being Blacklisted
- Open Relay / Bot
Your server may have been used to send spam.
- Insufficient Auth
Missing SPF/DKIM/DMARC makes abuse easier.
- Sudden Volume Spike
Sending bursts from low-reputation IPs trigger spam filters.
- Neighbor IP Effect
Bad IPs in the same /24 block can also harm your reputation.