Mail server address has no reverse DNS name
What this check looks for
The address behind one of your mail servers has no reverse DNS entry. Many receiving systems treat that as a spam signal when this machine also sends mail.
Why it matters
If this host sends as well as receives, missing or mismatched reverse DNS is one of the most common reasons for mail being rejected or filtered outright.
When the check passes, your report says: “Every mail server address has a reverse DNS name”.
What it costs your score
When this check fails it removes 2 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
- low
- Default confidence
- confirmed
- Status when triggered
- warn
- Deduction
- 2 points
- Family cap
- email-transport.mx · 30
- Category
- Email transport
- Module
- Email mx
- Fix owned by
- ip provider
- In the ruleset since
- 2026.09
How to fix it
Ask whoever owns the IP address to publish a PTR record matching the mail server's hostname.
Outbound mail from an address with no reverse DNS is filtered aggressively by large receivers.
Find who owns
‹address›— usually your hosting or cloud provider, not your DNS host.Set the reverse DNS entry for the address to
‹expected hostname›in their control panel.Confirm the name resolves forward to the same address, so the pair matches.
How to confirm it worked
dig +short -x ‹address› — expect ‹expected hostname›
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
A PTR lookup for ‹address› (the address of MX host ‹mx target›) returned ‹resolution result›. RFC 1912 §2.1 requires every internet-reachable address to have a matching PTR record, and the widely applied convention is that the PTR name resolves forward to the same address (a confirmed forward-confirmed reverse DNS pair). Reverse DNS is delegated by whoever owns the address block, so this is normally set through the hosting provider rather than in your own zone.
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
- 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