Check an IP address (or a domain - we'll resolve its A record) against several well-known DNS-based spam blacklists.
DNS-based blacklists (RBLs/DNSBLs) let mail servers reject or flag messages from IPs with a history of sending spam, running an open relay, or being part of a botnet. Being listed - even on one list - can mean your legitimate email gets silently dropped or sent to spam. Enter your mail server's IP (or its hostname) above to check it against several independently-run lists at once.
Blacklists are one piece of the puzzle. See the full picture with our Email DNS Check.
Run the Email DNS CheckDNS-based blacklists (DNSBLs or RBLs) let mail servers reject or flag messages from IP addresses with a history of spam, open relaying, or botnet activity. A lookup works by querying the reversed IP octets as a subdomain of the blacklist's zone (for example 2.0.0.127.zen.spamhaus.org) and checking whether an A record comes back. Being listed on even one well-used list can mean legitimate mail silently lands in spam or gets rejected outright.
Several major blacklists, Spamhaus in particular, rate-limit or block free queries coming from datacenter and cloud-hosting IP ranges as part of their fair-use policy. A result of "unknown" on this checker most often reflects that rate limiting rather than the IP actually being clean, which is why this tool reports three distinct states instead of collapsing unknown into clear.
If you need related checks, try Email DNS check validator and Check Email deliverability score online.
Clear means the list returned a definitive not-listed (NXDOMAIN) answer. Unknown means the query did not get a usable answer at all, often because the list is rate-limiting or blocking automated lookups from hosting networks. Treat unknown as inconclusive, not as a clean bill of health.
You often only know the domain, not the exact sending IP. This tool resolves the A record for you first. If your mail actually goes out through a different server (a marketing platform, a relay), check that server's IP directly instead.
It depends on the list. A handful of major, widely-used lists (like the one this tool checks first) affect a large share of mail providers, while smaller or more obscure lists have limited real-world impact. Fix the underlying cause first, then follow that specific list's own delisting process.
Shared hosting and cloud IP ranges are sometimes listed because of what a previous tenant of that IP did, not anything you did. This is common with dynamic cloud IP allocation and is worth raising with your hosting provider if it keeps recurring.
No, blacklisting and authentication are separate systems. A clean SPF/DMARC/DKIM setup prevents others from spoofing your domain, but it does not remove an IP-based blacklist entry. Each list has its own removal process, usually reachable from the list's own website.
Both. Check the new sending IP before switching to it if possible, and check it again shortly after cutover, since a small number of blacklists specifically target IPs that just started sending volume.