What is a PTR record? Reverse DNS clearly explained

A PTR record links an IP address back to a hostname, which forms the basis of reverse DNS: the opposite of a normal A or AAAA lookup. If you run your own mail server or VPS, a PTR record is essential. Without a correct PTR record, major email providers such as Gmail, Yahoo, and Microsoft reject your outgoing mail or send it to the spam folder. This article explains what a PTR record is, how reverse DNS works, who sets it up, and how to check it yourself.

What is a PTR record?

A PTR record (pointer record) points an IP address back to a hostname. It is the mirror image of the A record, which points a hostname to an IPv4 address, and the AAAA record, which points to an IPv6 address. Because it works from address to name, it is known as reverse DNS or a reverse lookup.

In the DNS standard, it is record type 12. It is defined in RFC 1035 from 1987, the same standard that describes the A record and the rest of classic DNS. Its value is a full hostname (an FQDN) such as mail.yourdomain.com, not an IP address and not a pointer to another alias.

Why a PTR record matters for email

Its primary use is email delivery. On every incoming connection, a receiving mail server checks the IP address the message comes from. If that IP address has no reverse DNS entry, or points to a generic or mismatched name, many servers treat your mail as suspicious.

Since 1 February 2024, Google and Yahoo have made valid reverse DNS a requirement for anyone who sends large volumes of email: the sending IP address must have a valid, meaningful PTR record. Microsoft (Outlook.com and Hotmail) also rejects mail from IP addresses that have none. For your own mail server, having one correctly configured is therefore a requirement, not optional.

Keep in mind that a PTR record is separate from SPF, DKIM, and DMARC. Those three handle authentication of your domain, while it works at the level of the IP address. You need both: flawless SPF, DKIM, and DMARC will not make up for a missing reverse entry.

How reverse DNS works: the reverse zone

Reverse DNS uses a separate branch of DNS: the reverse zone. For IPv4 this is the in-addr.arpa domain; for IPv6 it is the ip6.arpa domain.

For IPv4, the four parts (octets) of the IP address are placed in reverse order and followed by .in-addr.arpa. The reverse entry with the hostname then lives at that name. The reversed order reads awkwardly, but it lets a network block be delegated cleanly.

For IPv6, the full address is written out as 32 separate hexadecimal digits (nibbles), placed in reverse order, and followed by .ip6.arpa. Here is an example of each:

IPv4
  IP address:    192.0.2.10
  Reverse name:  10.2.0.192.in-addr.arpa
  PTR value:     mail.yourdomain.com

IPv6
  IP address:    2001:db8::1
  Reverse name:  1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa

Who sets up the PTR record?

This is where the biggest misunderstanding lies. You cannot add a PTR record to your own domain's DNS zone the way you add an A or MX record. It does not belong to your domain but to the IP address, and the reverse zone for an IP address is managed by the owner of the IP block: your hosting or VPS provider, or in some cases your internet provider.

In practice, you request it from whoever you rent the IP address from. Some providers offer a field for this in the customer panel; others set it on request. If you have a residential or dynamic IP address from a home connection, you usually cannot set one at all, and such addresses are often blocked for outgoing email anyway.

At LJPc hosting you manage your forward records, such as A, AAAA, CNAME, and MX, yourself through the DNS management panel, but a PTR record falls under the reverse zone of the IP address. If you need one for an IP address hosted with LJPc hosting, contact support.

Setting up a PTR record, step by step

The order below prevents most mistakes. Work through the steps and only check the result afterward.

1. Make sure you have a fixed (static) IP address for which you are allowed to set reverse DNS.
2. Choose the hostname of your mail server, for example mail.yourdomain.com.
3. Create a forward record: an A record for IPv4 or an AAAA record for IPv6, pointing that hostname to the IP address.
4. Request the PTR record from your provider, using exactly the same hostname as its value.
5. Configure your mail server to identify itself with that same hostname (the HELO/EHLO name).
6. Check the result with the tools later in this article.

Use one clear PTR record per IP address. Multiple entries on the same IP address are technically allowed, but they cause confusion for spam filters and log files.

Forward-confirmed reverse DNS (FCrDNS)

Mail servers check not only whether a PTR record exists, but also whether it is correct in both directions. This is called forward-confirmed reverse DNS (FCrDNS), or a full-circle check:

• The IP address has a PTR record that points to a hostname.
• That hostname has an A or AAAA record that points back to exactly the same IP address.

When both directions match, the check passes. That is why it matters that the reverse entry, the forward record, and the HELO/EHLO name of your mail server all use the same hostname. If they differ, your email risks being rejected or marked as spam.

Checking your PTR record

You can look up reverse DNS yourself with standard DNS tools. Replace the example IP with your own address.

On Linux and macOS, use dig with the -x option:

dig -x 192.0.2.10 +short

On Windows, use nslookup:

nslookup 192.0.2.10

The host command works too:

host 192.0.2.10

Then confirm that the returned hostname resolves to the same IP address with a normal forward lookup, for example dig mail.yourdomain.com +short. If both resolve to the same address, your reverse DNS is in order.

Common problems

Most complaints about reverse DNS come down to a handful of causes.

A correctly configured PTR record is a small step with a big effect on your email delivery. Not sure how to proceed? Contact support.