What an IP blacklist check does
A DNS-based blocklist, often called a DNSBL, lets a mail system ask whether an IP address appears in a database maintained by a list operator. This page reverses the four IPv4 octets and checks five public DNSBL zones: Mailspike, PSBL, SpamCop, DroneBL, and UCEPROTECT Level 1. These are the only lists included in this check; it does not query every blacklist. The lists have different data, detection methods, and removal rules. A result therefore says only what those operators returned at the time of the query; it does not predict whether a recipient will accept a message.
Three states are shown for every list. Listed means that the DNS query returned a record in that list's zone. Not listed means the query completed and returned no address record. Couldn't check means the resolver failed or the lookup could not complete within the endpoint's short overall time budget. A timeout or resolver policy can prevent a result; it should never be read as a clean result. Each list name links to the operator's own lookup or removal page, where you can see its explanation and current status.
Why an address might appear
Blocklists can record direct spam sources, compromised devices, suspicious activity, or an address range that is not meant to send mail directly to receiving servers. The same public IP may be shared by many customers behind carrier-grade NAT or may be reassigned to a different subscriber. Mailspike classifies reputation levels, while UCEPROTECT Level 1 is intended to identify an individual IPv4 address. Their criteria and update cycles are not interchangeable. A single listing does not prove that you personally sent unwanted mail.
Residential internet addresses are often expected to send email through an authenticated provider or ISP relay rather than connect directly to every recipient's mail server. If you are checking the address shown by a home connection, a policy listing can be normal. If you operate a mail server, check the server's actual outbound address, mail logs, reverse DNS, SPF, DKIM, and DMARC before taking action. A browser IP is not always the same as the server that sends your mail.
What to do next
Open the affected operator's own page and follow its evidence and removal process. If the listing points to a shared provider range, contact the ISP or hosting company because you may not control the address. For a dynamic home address, the provider may rotate it or offer a mail relay. Avoid paid removal services that promise to erase a listing without reviewing the list operator's rules. Read our blacklist guide for the difference between a DNSBL result and mail delivery, and our CGNAT guide for shared public addresses.
Frequently asked questions
Does “listed” mean my email is blocked everywhere?
No. Mail providers choose which reputation sources to use and how strongly to weigh them. A listing can matter to one receiver and be ignored by another.
Can you check IPv6?
Not yet. This tool checks IPv4 DNSBL zones only. Use an operator's own checker if it offers IPv6 support.
Why does a lookup say “couldn't check”?
The server's resolver may time out, restrict the query, or lack DNS lookup support. Retry later or use the linked list operator's checker.
Is my address stored?
The address is sent to the site's server and appears in the DNS query sent through the host's resolver to each list. The tool does not save a lookup history; ordinary hosting logs may apply.
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