Address reputation
Checks an address against public DNS blocklists — the same ones mail servers consult when deciding whether to accept a message from you.
The check is made with DNS queries from our server. No connection is opened to the address itself.
A DNSBL is a list of addresses published over DNS, which mail servers consult before accepting a message. Being listed does not mean you did anything: addresses are listed for sending spam, for running an open relay or open proxy, for belonging to a range an operator has flagged as dynamic residential space, or simply because a previous holder of the address misbehaved and the listing has not aged out.
The lists differ in temperament, and that matters when you read the result. Spamhaus is conservative and widely trusted, and a listing there is the one worth acting on. Some other zones list whole ranges by policy rather than by observed behaviour, so appearing on one of them says more about your hosting provider than about you. One listing out of many is routine; several serious ones together is a delivery problem you will have already noticed.
Both failure modes give a confident wrong answer, which is why they are worth stating.
The first: large operators answer queries coming from cloud resolvers with a code in the 127.255.255.x range. That code means "you have exceeded your query limit", not "this address is listed" — and reading it as a listing tells someone their clean address is blacklisted.
The second: a zone that has shut down answers NXDOMAIN to everything. Naive code reads that as "not listed" and declares any address on earth clean, on the word of a list that checked nothing.
So each zone is first asked about 127.0.0.2, the address every DNSBL publishes as permanently listed. A zone that cannot confirm its own test record is marked "no answer" and its silence about your address is discarded rather than counted as a pass. The SORBS zone has been removed from the list entirely — it closed in 2024, and a check against a dead zone is worse than no check.
Find the cause first: a compromised machine, a misconfigured mail server, an open relay, or an address inherited with history.
Fix the cause before requesting delisting. Every list will re-add you otherwise, and some are slower to remove you the second time.
Use the delisting form the listing zone publishes; there is no central authority that can remove you from all of them.
Check that the port your mail server exposes is what you intend with the port scanner, and look up who the address belongs to with the IP lookup.
A blocklist of IP addresses published through DNS, which mail servers query before accepting a message. It is the standard mechanism behind most spam filtering at the connection level.
Common causes are spam sent from a compromised machine, an open relay or open proxy, a range an operator classifies as dynamic residential space, or a previous holder of the address whose listing has not yet expired.
Fix the cause, then use the delisting form the specific zone publishes. There is no central registry: each list is operated independently and removes addresses on its own terms.
Usually not. Lists differ enormously in how aggressively they add addresses, and some list whole ranges by policy. A Spamhaus listing, or several serious lists at once, is what actually affects delivery.
Because it did not confirm its own test record. That means either a rate limit or a dead zone, and in both cases its answer about your address is unreliable — so we discard it rather than report a clean result we cannot stand behind.
Rarely. DNSBLs are consulted by mail servers, so the direct effect is on email delivery. Some firewalls and forum platforms use reputation data as well, so a heavily listed address can meet friction elsewhere.