Reverse DNS mismatch
PTR (reverse DNS) for a sending IP is missing or does not match the forward hostname used in mail.
Problem summary
PTR (reverse DNS) for a sending IP is missing or does not match the forward hostname used in mail.
Symptoms
- Receivers defer or reject citing reverse DNS
- PTR is missing, generic, or does not match the HELO/forward name
Possible causes
- Misconfiguration
- Incomplete rollout
- DNS propagation delay
How to diagnose
- Confirm the symptom in headers or reports
- Inspect the relevant DNS records
- Validate with a trusted checker
How to fix
- Correct the DNS or signing configuration
- Re-test and confirm alignment where required
How to verify
- Re-check DNS
- Send a test message
- Confirm expected authentication results
Prevention
- Document changes
- Monitor reports after deployment
When to escalate
- Production mail is failing authentication after a change window