NXDOMAIN - Expired Domains Glossary

NXDOMAIN stands for "Non-Existent Domain." It's a DNS response code (RCODE 3) that means the queried domain name doesn't exist in the DNS system at all. Not "server is down." Not "no website here." The domain itself is not registered.

How NXDOMAIN works

When you query a DNS resolver for a domain, the resolver eventually reaches the authoritative nameserver for that domain's TLD. If the domain isn't in the registry's zone file, the server returns NXDOMAIN. This is different from other errors. A SERVFAIL means the DNS server had a problem. A NOERROR with no records means the domain exists but has no A record configured. NXDOMAIN is definitive: this name is not registered.

Some ISPs intercept NXDOMAIN responses and redirect you to a search page instead. That's called NXDOMAIN hijacking. It's annoying for users and problematic for tools that rely on accurate DNS responses. That's why bulk DNS checking tools use trusted public resolvers like Google (8.8.8.8) or Cloudflare (1.1.1.1) instead of ISP resolvers.

NXDOMAIN in the expired domain pipeline

NXDOMAIN is the key signal CatchDoms uses to find deleted domains that are available for registration. Here's how it works. Historical crawl data from Common Crawl provides millions of domains that were once active websites. A mass DNS check with tools like massdns queries all of them. Domains returning NXDOMAIN are potentially deleted and up for grabs.

But NXDOMAIN alone isn't enough. A domain might have just expired and still be in the redemption period. Or the DNS server might have timed out, giving a false signal. That's why the next step is an availability check via registrar APIs to confirm the domain can actually be registered. The combination of NXDOMAIN plus confirmed availability is what makes a regfree domain.

Frequently asked questions

Does NXDOMAIN mean a domain is available to register?

Not necessarily. NXDOMAIN means the domain isn't in the DNS system right now, but it could still be in a redemption period or pending delete. You need to confirm availability through a registrar API or WHOIS lookup before you can actually register it.

What is the difference between NXDOMAIN and SERVFAIL?

NXDOMAIN means the domain doesn't exist at all in the registry. SERVFAIL means the DNS server had a problem processing your query. A SERVFAIL doesn't tell you anything about whether the domain is registered or not.

Why do some ISPs redirect NXDOMAIN responses?

Some ISPs intercept NXDOMAIN and redirect you to their own search or advertising page instead of showing an error. It's called NXDOMAIN hijacking. That's why bulk DNS tools use trusted public resolvers like Google (8.8.8.8) or Cloudflare (1.1.1.1) to get accurate responses.