mx.ptr.hostname_differs
PTR Hostname Differs From MX Hostname
What we check
We compare each MX IP's forward-confirmed PTR hostname against the MX hostname the domain publishes. This finding is emitted when the PTR hostname is valid (FCrDNS passes) but names a different host than the MX record.
This is a per-IP check — each resolved IP is evaluated independently.
What this finding means
The IP's reverse DNS points to a hostname that differs from the MX hostname. For example, the domain publishes mail.example.com as its MX target, the IP resolves, but the PTR record for that IP names filter42.provider.example.net. FCrDNS succeeds (the PTR hostname resolves back to the same IP), but the names do not match.
This is extremely common and usually harmless. Large email providers and spam-filtering services route MX traffic through shared infrastructure with its own PTR namespace:
- Google Workspace MX IPs have PTRs like
*.1e100.net - IONOS MX IPs have PTRs like
*.kundenserver.de - Spam filter front-ends (Barracuda, Proofpoint, Mimecast) use their own PTR names
Why it matters
- Context, not a problem. A differing PTR name with valid FCrDNS is standard practice for hosted and filtered mail. It is surfaced so administrators who cross-check against stricter tools see the raw values without confusion.
- No delivery impact. No major email provider penalizes a PTR mismatch with the MX hostname as long as FCrDNS passes.
Evidence example
MX target: mail.example.com → 192.0.2.1
PTR: filter42.provider.example.net
FCrDNS: filter42.provider.example.net → 192.0.2.1 ✓
PTR hostname differs from MX hostname — informational only