MX record points at a CNAME
What this check looks for
One of your mail server records points at an alias rather than a real host. The standard forbids this, and some sending servers refuse to follow it.
Why it matters
It usually works and occasionally does not, which makes the resulting delivery failures rare, intermittent and very hard to trace.
When the check passes, your report says: “Every MX record points at a real host, not an alias”.
What it costs your score
When this check fails it removes 12 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
- confirmed
- Status when triggered
- fail
- Deduction
- 12 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
Point the MX at a hostname that has A/AAAA records directly.
An aliased MX target is prohibited and is not followed by every sender.
Find the hostname
‹mx target›ultimately resolves to.Either point the MX at that hostname, or replace the CNAME with A/AAAA records of its own.
How to confirm it worked
dig ‹mx target› — expect A/AAAA records directly, with no CNAME in the answer section
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› resolves through a CNAME. RFC 5321 §5.1 states the MX target must resolve to an address record and must not be an alias; RFC 2181 §10.3 makes the same prohibition for records referenced by name.
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 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)
- Only one mail server host is published