What does it mean to be on a list?

A receiver that uses this list will probably reject mail from the affected IP or domain or file it as spam. The entry must be removed through the list's delisting page, this tool cannot trigger that.

How do I remove my IP from a blocklist?

First fix the cause of the listing (compromised account, spam script, open relay). Then fill in the delisting form on the list's website. Some lists remove entries automatically after a few days without a new incident, others require a manual request.

My mail goes to spam, is that due to a blocklist?

Possibly, but not necessarily. A listing is one possible cause; just as common are missing or wrong SPF/DKIM/DMARC, poor reverse DNS or content-based spam signals. This check only clears up the blocklist part.

Why is not every existing list checked?

There are hundreds of small, barely used lists that almost no receiver queries, some with stale entries or paid delisting. This tool deliberately limits itself to established, widely used lists with stable availability.

What does 'No Spamhaus DQS key configured' mean?

Spamhaus blocks queries over public DNS resolvers without a personal key and then returns a misleading result. Without a key, only Spamhaus Zen and Spamhaus DBL are skipped, all other lists run normally.

Why are only the MX hosts checked for a domain?

IP blocklists rate sending mail servers, not web servers. For a domain the tool therefore checks the IPs of the MX records against the IP lists and the domain itself against the domain lists, not the IP of the website.

Blocklist Check

Check an IP or domain against well-known email blocklists (DNSBL/DBL).

Blocklists (DNSBL for IP addresses, DBL or URIBL for domains) collect senders that have been flagged for spam, open relays, compromised machines or abuse. If a receiving mail server uses such a list, it rejects mail from a listed IP or domain or files it as spam, regardless of whether SPF, DKIM and DMARC are clean. A listing is therefore one of the most common causes when delivery suddenly fails at scale.

What this tool checks

The input is an IP address or a domain. For an IP, only the IP lists are checked. For a domain, the tool first resolves the MX hosts (at most five) and checks their IPv4 addresses against the IP lists, and additionally runs the domain itself against the domain lists. It queries a curated selection of established lists (including Spamhaus Zen and DBL, SpamCop, SORBS, Barracuda, Mailspike, Blocklist.de, PSBL, SURBL, URIBL), each one individually: if one query fails, the others still run. For every hit, the return code is translated into plain words and the delisting link is shown.

Reading the result

Green means: found on none of the checked lists. A hit is a warning, not an error, because a listing is not a technical defect like an invalid certificate, it can be stale or disputed. Even so, every hit deserves a look and, if it exists wrongly, removal through the list itself. A single failed list query appears as a note (often a resolver limit, not a real result).

Background

The query method is described in RFC 5782: for an IPv4 address the octets are reversed and appended to the list zone, an A record in the 127.0.0.0/8 range means listed, NXDOMAIN means not listed, a TXT record gives the reason. RFC 6471 provides operators with operational guidance for maintaining such lists. Domain lists (DBL, URIBL, SURBL) use the same DNS pattern without an RFC of their own. Spamhaus requires a free DQS key for queries over public resolvers; without it only Spamhaus Zen and DBL are skipped.

Common problems and how to fix them

IP on a large list (Spamhaus, Barracuda). First stop the cause: a compromised mailbox, a script sending in an infinite loop, an open form without a rate limit, a misconfigured forward. Only then request removal through the list's delisting page, otherwise the next listing follows immediately.
Domain on a DBL or URIBL. Usually the domain is abused as a link target in spam mail or a subdomain was hijacked. Clean up the affected resource, lock compromised accounts, then request delisting.
New or freshly assigned IP. After a server move, the IP can carry an old reputation from its previous owner. Request delisting at the relevant lists and ramp up the sending volume slowly over the first few weeks (warmup).
Listing does not go away. Many lists remove entries automatically after a few days without a new incident. If the entry stays, the cause is still active, or it is a list with manual or paid delisting, whose significance is then questionable.
Only the web server is listed, not the MX. For email delivery, the IP that mail is actually sent from is what counts. Check which IP the mail server uses as its source address (visible in the SMTP Test) and enter exactly that one.

Common questions

What does it mean to be on a list?: A receiver that uses this list will probably reject mail from the affected IP or domain or file it as spam. The entry must be removed through the list's delisting page, this tool cannot trigger that.
How do I remove my IP from a blocklist?: First fix the cause of the listing (compromised account, spam script, open relay). Then fill in the delisting form on the list's website. Some lists remove entries automatically after a few days without a new incident, others require a manual request.
My mail goes to spam, is that due to a blocklist?: Possibly, but not necessarily. A listing is one possible cause; just as common are missing or wrong SPF/DKIM/DMARC, poor reverse DNS or content-based spam signals. This check only clears up the blocklist part.
Why is not every existing list checked?: There are hundreds of small, barely used lists that almost no receiver queries, some with stale entries or paid delisting. This tool deliberately limits itself to established, widely used lists with stable availability.
What does 'No Spamhaus DQS key configured' mean?: Spamhaus blocks queries over public DNS resolvers without a personal key and then returns a misleading result. Without a key, only Spamhaus Zen and Spamhaus DBL are skipped, all other lists run normally.
Why are only the MX hosts checked for a domain?: IP blocklists rate sending mail servers, not web servers. For a domain the tool therefore checks the IPs of the MX records against the IP lists and the domain itself against the domain lists, not the IP of the website.