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Reverse DNS and PTR Records Explained (and Why Mail Servers Need Them)

Ekim 4, 2026 · IpDnsHub ·
dns email reverse-dns

Forward and Reverse DNS

Normal (“forward”) DNS answers the question “what is the IP address of mail.example.com?”. Reverse DNS answers the opposite question: “what hostname belongs to the IP address 203.0.113.25?”. The answer is stored in a PTR (pointer) record.

You can check the PTR record of any address with our Reverse DNS Lookup.

How PTR Records Are Stored

Reverse DNS uses special domains. For IPv4, the address is written backwards under in-addr.arpa. The PTR record for 203.0.113.25 lives at:

25.113.0.203.in-addr.arpa.  PTR  mail.example.com.

For IPv6, every hexadecimal digit is reversed and separated by dots under ip6.arpa, which makes the names long but follows the same idea.

The address is reversed because DNS is read from right to left, from the most general part to the most specific. Reversing the address puts the network part first, so reverse zones can be delegated to whoever owns each address block.

Who Controls Your PTR Record?

This is the most common source of confusion. The PTR record is not managed where your domain’s DNS is managed. It is controlled by whoever owns the IP address — your hosting company, cloud provider or internet provider. To set or change it:

  • Cloud servers and VPS: most providers let you set the reverse DNS name in their control panel.
  • Dedicated servers: ask the hosting provider’s support.
  • Business internet connections: ask your internet provider. Home connections usually cannot have custom PTR records.

Why Mail Servers Care

Receiving mail servers check the reverse DNS of the connecting server as a basic trust signal. Many reject or heavily filter mail from addresses with no PTR record, or with a generic PTR such as 203-0-113-25.dynamic.isp.example that looks like a home connection. Gmail’s sender guidelines, for example, require sending IP addresses to have valid PTR records.

Forward-Confirmed Reverse DNS

The strongest setup is forward-confirmed reverse DNS (FCrDNS):

  1. The IP address has a PTR record, for example mail.example.com.
  2. That hostname has an A (or AAAA) record pointing back to the same IP address.

It is also good practice for the name your mail server uses in its SMTP greeting (HELO/EHLO) to match the PTR hostname.

Other Uses of Reverse DNS

  • Log readability: hostnames are easier to read than raw addresses in server logs.
  • Troubleshooting: router hostnames in a traceroute often include city codes or provider names.
  • Verifying crawlers: search engines recommend checking that a visitor claiming to be their crawler has a PTR record in their domain, confirmed by a forward lookup.

Quick Checklist for a Mail Server