Reverse DNS lookup (PTR)
A PTR record answers the opposite question: which name belongs to this address. Enter an IP address or a hostname — the PTR is looked up, checked for resolving back to the same address, and judged on whether it is good enough for a mail server.
How the reverse zone works
Reverse DNS is a separate tree of names: 203.0.113.10 becomes 10.113.0.203.in-addr.arpa, and an IPv6 address becomes a name under ip6.arpa. That zone belongs to whoever was allocated the address block — your host or ISP — not to the owner of the domain. This is why a PTR record is almost always changed in a hosting panel rather than next to your A and MX records.
FCrDNS: both directions must agree
A PTR record alone proves nothing. The receiver takes the name it returns and resolves it forward again: if the original address is not among the results, forward-confirmed reverse DNS fails. Without that step anyone holding an address could name it after someone else's host. This tool runs both halves and reports the outcome on its own line.
Why mail cares so much
Large mail systems reject or delay mail from addresses with no PTR — it is the cheapest available signal of a hastily configured server. A generated name like ip-203-0-113-10.provider.net passes the check but reads as 'a machine in a pool' and still costs reputation. For a sending server, the PTR name should match the name it announces in HELO.
Frequently asked questions
- The A record is set up, so why is there no PTR?
- They live in different zones. You publish the A record yourself, while the reverse zone is run by whoever holds the address block. Ask your hosting provider for the PTR, or set it in your server control panel.
- What is FCrDNS?
- Forward-confirmed reverse DNS: the name from the PTR record is resolved forward again and must point back at the same address. Agreement between the two is a standard expectation for mail servers.
- Can one address have several PTR records?
- Technically yes, but there is no reason to. The receiver uses whichever it gets first, which makes the name in remote logs unpredictable. Keep one — the name the server announces in HELO.
- How do I check the PTR of a domain's mail servers?
- Enter the server's hostname here: the tool resolves its addresses and checks the reverse zone for each one. The MX lookup page lists which hostnames a domain uses.