Email blacklist check
Looks an IP address or mail server up in the public blacklists — Spamhaus, SpamCop, Barracuda and others. If your outgoing mail is not reaching the inbox or is being refused outright, this is the first thing to check.
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What the email blacklist check measures
An email blacklist check looks one IPv4 address up in fifteen public DNS blocklists: Spamhaus ZEN, SpamCop, Barracuda, SORBS, PSBL, WPBL, blocklist.de, UCEPROTECT 1, DroneBL, s5h.net, CBL, GBUdb, SPFBL, Anonmails and Unsubscore. A DNSBL is a DNS zone used as a database: the octets are reversed, the zone appended and an A record asked for. No such name means not listed; an answer inside 127.0.0.0/8 means listed, its last octet the list's reason code, and the TXT reason is fetched for up to six listed or refusing lists.
A hostname is accepted and resolved first, and the page names the address actually checked. IPv6 is declined honestly: almost no public list publishes an IPv6 zone, and a clean result for a check never run would be worse than saying so. The queries go through Cloudflare's 1.1.1.1 from the IPVIEW server, and that path matters for one outcome below.
How to read the result
Four verdicts. Not on any blacklist: all fifteen answered and none knows the address. Listed on N blacklists, with a table of list, zone, code and reason. Not found on any list, but the check is incomplete: some lists gave no usable answer, and they are named rather than counted. The result cannot be trusted: a list returned an address outside 127.0.0.0/8, which on this network is a rewritten DNS answer, not a listing, and it outranks everything else because no other row is evidence while the resolver path is interfered with.
An answer in 127.255.255.x is not a listing either. That range is the list telling the querier something about the query: Spamhaus and CBL return 127.255.255.254 with the text Error: open resolver when asked through a large public resolver, and those rows appear under Refuse queries from this path. The address is neither clean nor listed there; ask that list from your own resolver.
When it is useful
Outgoing mail is bouncing or landing in spam. Check the sending address here, then Reverse DNS for its PTR name and Email security for the domain's SPF and DMARC; those three account for most refusals. The reason text usually says what got the address listed and where to request removal.
Before taking over a server or an address from a hosting provider, to learn whether it arrives with a history. 127.0.0.2 is the conventional test address that most DNSBLs list; it is accepted here as a self-test, though lists that refuse queries from public resolvers will show under Refuse queries.
Common questions
Why does the result say the check is incomplete?
One or more lists timed out, returned SERVFAIL or refused the query path. Silence is not a pass, so those lists are named and the verdict stops short of clean. Try again later, or ask the named lists directly.
What does 127.255.255.254 mean?
The list refusing to answer this query, not a listing. Spamhaus returns it to queries arriving via the large public resolvers, with the text Error: open resolver. Such rows are shown under their own heading so they are not read as blacklistings.
My address is listed. What do I do?
Read the reason text; it says which behaviour got the address listed, and most lists link to their removal process from there. Fix the cause first, since a relisting is held longer, and check Reverse DNS and Email security on the same server.
Limits. The DNS, WHOIS and SSL tools allow up to 20 requests a minute per IP address. Ping, traceroute and MTR send real packets to their target, so they allow 6 a minute.
The port check runs only against your own IP address. That is deliberate: the question people actually have, "is this port reachable from outside?", is answered by it, while this server cannot be used to scan anyone else's network.
Private and reserved addresses. These are refused by the tools that really connect to their target: the SSL check, ping, traceroute, MTR and the port check. The DNS tools have no such limit, because they only ask a nameserver a question and never connect to the address itself.