Reverse DNS Lookup
Find the PTR host name of an IPv4 or IPv6 address and check that it resolves back to the same address.
Reverse DNS of an IP address
PTR records from the public DNS, each checked against its own forward record.
What the Reverse DNS Lookup does
Reverse DNS Lookup turns an IP address back into a host name. It builds the in-addr.arpa name for an IPv4 address (or the nibble-by-nibble ip6.arpa name for IPv6), asks for its PTR records, and lists every name the owner of that address range has published.
It then does the part most reverse lookups skip: for each PTR name it fetches the forward A or AAAA record and checks that it contains the address you started with. When it does, the record is forward-confirmed, which is what mail servers look for before they trust a sending host. A PTR that points to a name resolving elsewhere is a common reason for mail landing in spam.
The tool refuses private, loopback and reserved addresses because they have no public reverse zone to query.
Step by step
- 01Paste an IPv4 or IPv6 address. Find it with the Domain to IP tool if you only have a domain.
- 02Press Look up. The PTR records are fetched from the public DNS along with their TTL.
- 03Read the Confirmed pill on each name: green means the name resolves back to this address.
- 04If your mail server's PTR is missing or unconfirmed, ask your hosting provider to set it; only the owner of the IP range can.
Common questions
The organisation that controls the IP range, which is usually your hosting or cloud provider, not your domain registrar. Most providers let you set it in their control panel under reverse DNS or rDNS; others do it on request. You cannot set it in your domain's own zone.
The PTR name resolves, through its own A or AAAA record, back to the same IP address. Receiving mail servers use this check (FCrDNS) to see whether a connecting host is what it claims to be. A name that fails it is treated with suspicion by Gmail, Outlook and most spam filters.
It is allowed, though unusual. Some providers publish a generic name alongside a customer name. Mail servers only need one of them to match the HELO name and resolve back; more than one can confuse some checks, so one is best.
For a web server, no. For a mail server, yes: it still confirms forward, but filters score generic cloud names lower than a name on your own domain such as mail.example.com. Set a custom reverse name with your provider for any host that sends mail.
Keep checking
Domain to IP
Find the IPv4 and IPv6 addresses behind a domain, the reverse DNS name of each and a hint at the hosting provider.
Free toolDNS Lookup
Look up the A, AAAA, CNAME, MX, NS, TXT, SOA, SRV and CAA records of any domain with their TTLs in one query.
Free toolBlacklist Checker
Check whether an IP or mail server is listed on Spamhaus, SpamCop, Barracuda, SORBS and ten more DNS blacklists.
Free toolSPF Checker
Validate a domain's SPF record: mechanisms, the include tree, the 10 DNS lookup limit, +all and syntax mistakes.
Free toolWHOIS Lookup
Registrar, creation and expiry dates, name servers, status and DNSSEC for a domain, or the network owner of an IP.
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