What it checks
How many nameservers the domain is delegated to. With only one, the whole domain stops resolving whenever that server is unreachable.
A pass means: The domain is served by more than one nameserver.
Possible findings
Only one nameserver
Severity: LowConfidence: ConfirmedKind: Recommended hardening
What we found
The domain is delegated to a single nameserver.
Why it matters
If that nameserver is unavailable, the whole domain stops resolving: websites, email and everything else under it.
How to fix it
Delegate the domain to at least two nameservers, ideally on separate networks. Most managed DNS providers supply two or more by default.