What this check looks at
Reverse DNS is the inverse of a normal lookup: given the connecting IP, what hostname does it claim (its PTR record)? Forward-confirmed reverse DNS (FCrDNS) goes one step further - it resolves that hostname back to an address and checks it matches the IP that connected. JoltMx checks:
- Whether the sending IP has a PTR record at all.
- Whether the PTR hostname forward-confirms back to the same IP.
- Whether that hostname also matches the EHLO name the server greeted with (best practice).
Why it matters
Legitimate mail servers have proper reverse DNS; throwaway spam sources usually don't. Gmail, Outlook and most large providers refuse mail outright from IPs with no PTR record, and several penalise mail where the reverse DNS doesn't forward-confirm. It's table stakes for running your own mail server.
How the diagnostic grades it
| Result | Severity | What it means |
|---|---|---|
| Forward-confirmed reverse DNS | Pass | The IP resolves to a hostname and back again. Ideal. |
| No reverse DNS | Critical | The IP has no PTR record - most large providers refuse the mail. |
| Does not forward-confirm | Warning | A PTR exists, but the hostname doesn't resolve back to the IP. |
| Private / uncaptured IP | Info | A local or missing address - reverse DNS doesn't apply (e.g. a test relay). |
How to fix it
- Ask your hosting or cloud provider to set a PTR record on the sending IP, matching your mail server's hostname.
- Make sure that hostname's A/AAAA record points back to the same IP so it forward-confirms.
- For the cleanest result, use the same fully-qualified name for the PTR and the EHLO greeting.