Reverse DNS (PTR Records): Why Your Mail Server Needs One

Reverse DNS (rDNS) maps an IP address back to a hostname — the opposite of a normal lookup — and a correct PTR record is essential for a mail server, because many receivers reject mail from IPs that lack one. It is one of the most overlooked causes of email delivery problems.

Forward vs reverse

A normal (forward) lookup turns a name into an IP via an A record. Reverse DNS turns an IP back into a name via a PTR record. It lives in a special reverse zone (in-addr.arpa for IPv4, ip6.arpa for IPv6) rather than in your normal domain zone.

Why mail servers demand it

Spam frequently comes from IPs with no proper reverse DNS, so receiving mail servers treat a missing or generic PTR as a red flag. Many will reject or heavily penalise mail from an IP that:

has no PTR record at all, or
has a generic PTR (a default ISP-style name), or
fails forward-confirmed reverse DNS (FCrDNS) — where the PTR name should resolve forward back to the same IP.

Getting rDNS right is a core part of email deliverability, alongside SPF, DKIM and DMARC.

Who controls the PTR

Crucially, you usually cannot set a PTR in your own domain zone — it is controlled by whoever owns the IP address block, typically your hosting provider or ISP. So on a VPS or dedicated server, you request the rDNS/PTR from your provider (or set it in a provider panel if offered). If you run your own mail on a VPS or dedicated server and need rDNS, that is the route.

Setting it up

Ensure a matching forward record — your mail hostname (e.g. mail.yourdomain.com) should have an A record to the IP.
Set the PTR to that hostname — request it from your IP/hosting provider so the IP resolves back to mail.yourdomain.com.
Verify FCrDNS — the forward and reverse should agree.

Check it with dig -x on the IP.

Frequently asked questions

Why can't I add a PTR record in my domain's DNS?

Because reverse DNS is controlled by the owner of the IP block, not the domain owner. For a server IP, that is your hosting provider or ISP, so you request the PTR from them rather than adding it to your own zone.

What is forward-confirmed reverse DNS?

It means the PTR name resolves forward back to the same IP — the reverse and forward records agree. Mail servers favour this consistency, so set your PTR to a hostname that has a matching A record to the IP.

Does rDNS matter for a normal website?

It is mainly critical for outbound mail servers. A typical website does not need a custom PTR to function, but any server sending email should have correct reverse DNS to avoid delivery problems.