DNSBL / RBL check
Check one public IPv4 address or all public IPv4 addresses resolved from a hostname.
A blocklist result is not a universal reputation verdict
DNS blocklists have different purposes, evidence sources and listing policies. An IP can appear in one list and not another, and the operational consequence depends on how each receiving mail system uses that data.
ZEN combines several Spamhaus IP datasets
Spamhaus ZEN combines SBL, CSS, XBL and PBL data. Its 127.0.0.x return code identifies the category involved, so the portal interprets the code instead of treating every DNS answer as the same kind of listing.
Spamhaus 127.255.255.x codes are errors, not listings
Spamhaus documents special error responses for an invalid DNSBL query, queries through public/open resolvers and excessive query volume. These responses must never be interpreted as evidence that the checked IP is listed.
SpamCop is a fast-changing, aggressive blocklist
The SpamCop Blocking List is driven by reported email and other signals and automatically removes entries as reports stop. SpamCop itself recommends using the SCBL carefully, preferably as part of filtering or scoring rather than as an isolated absolute verdict.
A hostname can represent multiple sending IPs
When a hostname has multiple A records, reputation belongs to each IP separately. This version therefore checks up to eight unique public IPv4 addresses instead of silently choosing a single DNS answer.
This checker intentionally focuses on IPv4
The two providers shown here do not have equivalent IPv6 query behavior in this implementation. Keeping the tool explicitly IPv4 avoids presenting incomplete SpamCop coverage as if both providers supported the same IPv6 lookup.