MX host does not resolve to an address
What this check looks for
One of your mail servers is named in DNS but that name has no address, so nothing can connect to it. Mail directed there fails.
Why it matters
If this is your only mail server, all inbound mail is failing right now. If it is a backup, it will fail exactly when you need it.
When the check passes, your report says: “Every MX host resolves to an address senders can reach”.
What it costs your score
When this check fails it removes 20 points from your Email transport score, before the status, confidence and repeat multipliers are applied. Email transport carries a weight of 8 in the overall score.
It shares the email-transport.mx family ceiling of 30 points: however many findings that family produces, together they cannot remove more than that from Email transport. One underlying problem showing up in several places is still one problem.
- Severity
- high
- Default confidence
- confirmed
- Status when triggered
- fail
- Deduction
- 20 points
- Family cap
- email-transport.mx · 30
- Category
- Email transport
- Module
- Email mx
- Fix owned by
- dns host
- In the ruleset since
- 2026.09
How to fix it
Publish A/AAAA records for the MX host, or remove the MX record that names it.
An MX target with no address is an entry that can never accept mail.
Check
‹mx target›for a typo against your provider's documentation.If the host is retired, delete its MX record — a dead backup MX also delays delivery.
If the host is live, publish its A and AAAA records.
How to confirm it worked
dig +short A ‹mx target› — expect at least one address
A named slot like ‹domain› — and the braces left in the configuration below — is filled in with your own values when this rule appears on a report.
Technical detail
The MX target ‹mx target› for ‹domain› returned no A or AAAA records (‹resolution result›). RFC 5321 §5.1 requires the target to resolve to an address record; a sender that cannot resolve it treats the host as unusable and moves to the next preference, or bounces if there is none.
Standards and references
Test this on your domain
Run the check that produces this finding, on its own, against any domain.
Other email mx checks
- Two MX hosts share the same preference value
- MX record points at a CNAME
- MX record points at an IP address instead of a hostname
- Mail server address has no reverse DNS name
- No MX record — this domain cannot receive email
- Every mail server resolves to the same address
- Domain publishes a null MX (receives no mail)
- Only one mail server host is published