DNSprobe Wiki - IP
Reverse DNS (PTR)
Reverse DNS maps an IP address back to a hostname through a PTR record.
PTR records are commonly checked for mail servers, security logs, network diagnostics, and IP reputation.
A missing reverse record does not always prevent a website from working, but it can cause SMTP warnings or make operations harder.
1. Overview
For IPv4, reverse DNS uses the in-addr.arpa zone. For IPv6, it uses ip6.arpa.
PTR records are usually managed by the provider controlling the IP block, not by the domain's regular DNS zone.
2. What DNSprobe checks
DNSprobe queries the PTR name associated with the tested address.
- Reverse lookup from IP to hostname.
- Display of the returned hostname when one exists.
- Warning when no public PTR is available.
3. Interpreting results
A useful PTR should point to a hostname consistent with the address purpose.
- Info: a reverse hostname was found.
- Fail: no PTR was found or the response simply returned the IP.
- For email, the PTR hostname should also resolve back to the IP via A or AAAA.
4. Best practices
- Ask the IP provider to configure the PTR record.
- Use a stable, descriptive hostname, especially for SMTP servers.
- Avoid generic PTR names when mail reputation matters.
- Verify that forward DNS for the PTR name returns the address.
5. Manual tests
Test reverse and forward DNS.
dig -x 203.0.113.10 +short
dig A mail.example.com +short
dig AAAA mail.example.com +shortTo change a PTR record, you usually need to contact the host or provider of the IP block.