Demo
Demo

Knowledge base

dns-nameserver verifiedimportantWritten by the Hub

Name servers used for resolution

in the configuration this is a linedns-nameserver: …

Name servers the engine queries, overriding whatever the system's resolver configuration says.

Values

Values
comma-separated resolver addresses
applying
restart required
where it can be set
in the config file · with a startup flag · as an environment variable

In detail

Without it the engine follows /etc/resolv.conf, which on a provider's image is usually a public resolver — 8.8.8.8 on our node. For a machine that resolves an MX record for every recipient domain, that has three costs: public resolvers throttle heavy clients, every lookup discloses what the customer is sending to and when, and the cache that answers is shared with the world rather than warmed by our own repeated queries. Pointing this at our own resolvers fixes all three, and Hub already runs name servers for the outbound side of DNS. The directive is one of the eighteen missing from the help output, found by probing the binary — which is also why nobody has been using it.

What happens if you get it wrong

Left unset on a provider image with a public resolver.MX lookups are rate-limited under load, and the pattern of a customer's sending is visible to a third party.verified by experiment · inference
Pointed at a resolver that goes down.Every domain stops resolving; messages fail with 5.4.4 and go straight to failure without retries — a resolver outage becomes a wave of permanent failures.verified by experiment · inference