Quickly perform a reverse IP lookup to see the PTR record and domain mapping of any IP address. Verify DNS configuration and ensure server accuracy
A reverse DNS lookup finds the hostname assigned to an IP address. Where a normal (forward) lookup turns dns.google into 8.8.8.8, a reverse lookup turns 8.8.8.8 back into dns.google, using a PTR record. Mail servers, logging tools and network diagnostics all rely on it.
Reverse DNS records live in special zones. For IPv4 the address is reversed and placed under in-addr.arpa, so the PTR record for 203.0.113.7 is stored at 7.113.0.203.in-addr.arpa. IPv6 uses the address's hex digits, reversed, under ip6.arpa. These zones are controlled by whoever holds the IP block (your ISP, hosting or cloud provider), not by the owner of a domain name.
From a terminal: dig -x 8.8.8.8 on macOS or Linux, or nslookup 8.8.8.8 on Windows.
mail.example.com means the IP's owner set a specific PTR record, which is what you want for a mail server.203-0-113-7.dynamic.isp.example is an ISP default. Many mail servers treat such names as home connections and reject mail from them.For mail servers, check that the result is forward-confirmed: run an A Lookup on the hostname and make sure it returns the same IP. Gmail and other large providers require this for sending servers.
You can't set reverse DNS in your domain's DNS zone. It is set by the holder of the IP address:
After a change, the old PTR can stay cached until its TTL expires; the DNS Propagation Checker (PTR type) shows when resolvers have the new name.
Receiving mail servers check that the sending IP has a PTR record and that its hostname resolves back to the same IP. A missing or generic PTR is a strong spam signal, and Gmail rejects or filters mail from IPs without one.
It is technically possible but should be avoided. Many systems read only the first answer, so give each IP a single PTR that matches the hostname the server identifies itself with.
Reverse DNS returns the one hostname set in the IP's PTR record. A "reverse IP lookup" usually means finding every website hosted on an IP, which needs a database of crawled sites rather than DNS.
Your provider controls the reverse zone for its addresses and fills it with default names. Ask them to set a custom PTR if you run a mail server on that IP.