Only one mail server host is published
What this check looks for
All of your inbound mail depends on a single server. If it is unreachable, senders queue messages and eventually give up, and some mail is lost.
Why it matters
Senders typically retry for a few days, so a short outage is survivable — but a longer one, or a sender with a short retry window, means messages bounce.
When the check passes, your report says: “More than one mail server host is published”.
What it costs your score
When this check fails it removes 8 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
- medium
- Default confidence
- high
- Status when triggered
- warn
- Deduction
- 8 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 at least one backup MX, or confirm your provider's single name is multi-homed.
One host means one point of failure for everything sent to you.
If you use a hosted provider, check their documentation — many publish several MX names and you may have entered only one.
If you run your own mail server, add a second host at a higher preference number, on separate infrastructure.
A backup MX must be configured to relay to the primary and to apply the same anti-spam checks, or it becomes a way around them.
How to confirm it worked
dig +short MX ‹domain› — expect two or more targets
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
‹domain› publishes ‹mx count› distinct MX target(s) resolving to ‹address count› address(es). RFC 5321 §5.1 describes trying MX hosts in preference order; with a single host there is nothing to fall back to. Note that a hosted provider often publishes one name that resolves to many addresses across regions, which is genuine redundancy — this finding is downgraded when we can confirm that.
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
- MX host does not resolve to an address
- No MX record — this domain cannot receive email
- Every mail server resolves to the same address
- Domain publishes a null MX (receives no mail)