mx.ptr.multiple_records
Multiple PTR Records on MX IP
What we check
We count the number of PTR records for each MX IP address. Best practice per M3AAWG recommendations is a single PTR record that names the server's canonical hostname.
This is a per-IP check — each resolved IP is evaluated independently.
What this finding means
The MX IP address has more than one PTR record. While DNS allows multiple PTR records for a single IP, and all of them may individually pass FCrDNS, the configuration is unusual for a mail server and can cause ambiguity about the server's canonical identity.
Why it matters
- Ambiguous identity. With multiple PTR records, different DNS resolvers may return them in different orders. Software that uses PTR for banner verification or logging may see inconsistent results.
- Not a delivery problem. No major email provider rejects mail solely because an IP has multiple PTR records. This is an informational finding surfaced for completeness.
- Usually a hosting artifact. Multiple PTR records often appear on shared hosting IPs that serve multiple domains, or when an old PTR was not cleaned up after a hostname change.
Evidence example
$ dig +short -x 192.0.2.1
mail.example.com.
legacy.example.com.
Two PTR records for the same IP — best practice is a single canonical name