mx.target_unresolvable
MX Target Hostname Does Not Resolve
What we check
We resolve each MX target hostname to its A and AAAA records. This finding is emitted when an MX target hostname definitively does not resolve — the DNS lookup returns NXDOMAIN or an empty answer with no A or AAAA records.
What this finding means
An MX record points to a hostname that does not exist in DNS or has no address records. Sending servers cannot determine an IP address for this MX target and will skip it. If other MX records point to working servers, mail still flows through them — but this target is dead weight. If all targets are unresolvable, the domain cannot receive mail at all (mx.no_usable_targets).
Why it matters
- Reduced redundancy. A dead MX target provides no failover. If the working MX targets go down, this one cannot pick up the load.
- Delivery delays. Some sending servers try MX targets in priority order and wait for a connection timeout before moving to the next one. An unresolvable target wastes time.
- Migration remnant. This commonly occurs when a server is decommissioned but its MX record is left behind, or when a hostname is misspelled in the MX record.
How to fix
Check the hostname spelling in the MX record — a typo is the most common cause:
dig +short MX example.com # Look for misspelled hostnamesIf the server still exists, add the missing A/AAAA record:
mail.example.com. IN A 192.0.2.1If the server was decommissioned, remove the MX record pointing to it.
Verify the fix:
dig +short A mail.example.com # Expected: the mail server's IP address
How it's graded
An unresolvable MX target carries a 20-point deduction in the MX category. See Grading Methodology for the full scoring model.
Evidence example
$ dig +short MX example.com
10 mail.example.com.
20 old-backup.example.com.
$ dig +short A old-backup.example.com
(empty — NXDOMAIN)
MX target "old-backup.example.com" does not resolve