Email Blacklist (DNSBL) Check
Check whether an IP is listed on major DNSBL blacklists.
The Email Blacklist (DNSBL) Check tells you in real time whether an IPv4 address has been reported as a spam source and listed on major blocklists. When a mail server's IP gets listed, the messages it sends can be rejected by receiving servers or dropped into spam — so even legitimate business email may fail to arrive.
This tool reverses the octets of the IP you enter and queries well-known DNSBL zones such as Spamhaus, SpamCop and Barracuda, showing the listing status of each at a glance. If your mail keeps bouncing or deliverability is dropping, start by checking whether your sending IP is on a blacklist, and review your domain's authentication setup with Email Deliverability Check.
How a DNSBL works
A DNSBL exposes a list of spam-sending IPs through ordinary DNS queries. You reverse the four octets of the IP you want to check (for example 1.2.3.4 becomes 4.3.2.1), append the blocklist zone name, and look up an A record. If an answer comes back, the IP is listed; if there is no answer (NXDOMAIN), it is clean.
Major blocklist zones
- zen.spamhaus.org: Spamhaus combined list (SBL, XBL, PBL); the most widely referenced.
- bl.spamcop.net: the report-driven SpamCop list.
- b.barracudacentral.org: the Barracuda reputation list.
- dnsbl.sorbs.net: the SORBS aggregate list.
- all.s5h.net: the s5h combined list.
Limits of public-resolver lookups
To keep server load low, this tool queries through a public DNS resolver (DNS over HTTPS). However, some DNSBLs — Spamhaus in particular — block or throttle queries coming from large public resolvers like Google and Cloudflare. In that case an IP that is actually listed may show as clean here. Treat the results as an indicative signal, and confirm important verdicts on each blocklist's official lookup page.