DNS & domains 2 min read

Normal DNS answers "what is the IP address of this name?". Reverse DNS answers the opposite question: "what is the name of this IP address?". The answer comes from a PTR record. Try it with our Reverse DNS lookup.

How reverse DNS works

PTR records live in special domains:

  • IPv4: the address is written backwards under in-addr.arpa. The PTR for 203.0.113.25 is looked up at 25.113.0.203.in-addr.arpa.
  • IPv6: every hexadecimal digit is reversed under ip6.arpa, which makes long names.

Because the reverse zone belongs to whoever holds the IP block, only your hosting provider or ISP can set the PTR record for your address, not your domain's DNS host.

Why reverse DNS matters

Email delivery

Receiving mail servers check the sending IP's reverse DNS. Many reject or flag mail when:

  • the IP has no PTR record,
  • the PTR name looks like a home connection (host-203-0-113-25.dynamic.example-isp.net),
  • the PTR name does not resolve back to the same IP.

The last check is called forward-confirmed reverse DNS (FCrDNS). Our tool shows whether an address passes it.

Logs and troubleshooting

Server logs and traceroutes show host names instead of bare numbers, which makes it easier to see which network traffic comes from.

How to set up reverse DNS for a mail server

  1. Choose a host name for the server, such as mail.example.com.
  2. Create an A record (and AAAA for IPv6) for mail.example.com pointing to the server's IP.
  3. In your hosting provider's control panel, set the PTR record of the IP to mail.example.com. If there is no option, open a support ticket.
  4. Make sure the mail server greets with the same host name (the HELO/EHLO name).
  5. Check the result with our Reverse DNS lookup: it should say Forward-confirmed.

Then set up SPF, DKIM and DMARC and check that the IP is not on a blacklist.

Frequently asked questions

Do I need reverse DNS for a website?

No. Reverse DNS matters for mail servers and some network services, not for websites.

Can one IP have several PTR records?

Technically yes, but it causes problems. Use one PTR record per IP address.

Why does my home IP have a long generated host name?

Providers create PTR records for all customer addresses automatically, usually including the IP and region.