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MX Health

Verifies the domain has a working MX configuration. The most common deliverability problem we see at this layer is missing A/AAAA records on MX targets, or a stale Null MX record left over from a previous configuration.

Applies to: URIBL and URI hosts.

How It Works​

We do an MX lookup on the domain and apply three sequential checks:

  1. The domain must have at least one MX record.
  2. The MX must not be a Null MX (0 ., RFC 7505), which explicitly says "this domain does not accept mail."
  3. At least one MX target must resolve to an A or AAAA record.

The check passes when at least one MX target is reachable. Unresolved MX targets are noted in the response but don't fail the check on their own (provided at least one target works).

Fails On​

  • No MX records at all.
  • Null MX (0 .).
  • All MX targets fail to resolve.