Defaults.Exposed › September 2026 census › v10 registry › Reverse DNS (PTR)
Reverse DNS (PTR)
Methodology v10 · canonical ID reverse-dns · Email Security · scored · census as of September 5, 2026
Helps your mail server look legitimate so messages aren't junked.
Definition
| Canonical ID | reverse-dns |
|---|---|
| Category | Email Security |
| Grade impact | Scored, counts toward the grade |
| Pass | The domain's mail-relevant IP has a PTR (reverse DNS) record. |
| Fail | No PTR record exists for the address. |
| Example (passing) | 10.0.113.203.in-addr.arpa. PTR mail.example.com. |
No-data rule: when this check couldn't be determined for a domain (timeout, SERVFAIL, redacted source) it returns N/A and is excluded from that domain's scoring denominator: "couldn't determine" is never counted as a failure. "Determined absent" is a real fail.
Prevalence across the census
77.8% of domains with a mail-relevant address have a PTR (reverse DNS) record (134,848,964 of 173,216,907, as of September 5, 2026).
Census denominator: 316,600,902 graded domains; this check is measured only against domains with a mail-relevant address (173,216,907). Aggregates only: never an individual domain's result.
Fix it
Plain-English impact, cost of ignoring it, and step-by-step remediation: defaults.exposed/fix/reverse-dns
Cite this check
Defaults.Exposed, "Reverse DNS (PTR) (reverse-dns)", Grading Methodology v10 (census as of September 5, 2026). https://defaults.exposed/methodology/reverse-dns
Permalink: https://defaults.exposed/methodology/reverse-dns ·
All 34 checks: v10 registry ·
Machine-readable: /methodology/checks.json ·
Licence: open data