mx.no_usable_targets
No Usable MX Target
What we check
We check whether any MX record points to a usable mail server. An MX target is unusable if it is an IP address literal (RFC 5321 §5.1 violation), a hostname that definitively does not resolve (NXDOMAIN or no A/AAAA records), or a Null MX mixed with other records. When the pure all-literal case applies, mx.all_targets_ip_literal is reported instead; this finding fires when at least one unresolvable hostname is part of the unusable mix.
What this finding means
The domain has MX records, but every single target is unusable — none can actually receive mail. This is functionally identical to having no MX records: sending servers have nowhere to deliver.
Why it matters
- Complete delivery failure. No sending server can deliver mail to this domain — every MX target is either an invalid literal, an unresolvable hostname, or part of an invalid Null MX configuration.
- Misleading DNS. MX records exist but point nowhere, which may cause senders to waste time attempting connections before giving up.
- Often a migration artifact. This typically occurs when a domain's mail infrastructure was decommissioned but the MX records were not cleaned up or replaced with a Null MX.
How to fix
If the domain should receive email, fix the MX targets so at least one points to a functioning mail server:
example.com. IN MX 10 mail.example.com.Ensure
mail.example.comhas A/AAAA records pointing to a running mail server.If the domain no longer accepts email, replace the broken MX records with a proper Null MX:
example.com. IN MX 0 .
How it's graded
No usable MX targets triggers an instant F grade for the MX category — the domain effectively cannot receive mail. See Grading Methodology for the full scoring model.
Evidence example
$ dig +short MX example.com
10 old-mail.example.com.
20 [192.0.2.99]
$ dig +short A old-mail.example.com
(empty — NXDOMAIN)
Both MX targets are unusable: one does not resolve, one is an IP literal