Reverse DNS is one of those quiet pieces of infrastructure that nobody notices until it breaks — and then your outgoing email starts landing in spam folders. If you run a mail server or any service that other systems connect to, PTR records deserve a few minutes of your attention.
Forward vs Reverse DNS
Normal (forward) DNS answers the question “what IP address does this hostname point to?” using A and AAAA records. Reverse DNS answers the opposite: “what hostname is associated with this IP address?” This mapping is stored in a PTR record.
Forward and reverse DNS are configured independently, which is why an IP can resolve a hostname forward while having no reverse record at all. For trust-sensitive services, you generally want both to exist and to match.
Why PTR Records Matter for Email
Mail servers are the biggest reason people care about reverse DNS. When your server connects to a recipient’s mail server to deliver a message, the receiving side often performs several checks:
- Does the sending IP have a PTR record at all? Many mail servers reject or heavily penalize connections from IPs with no reverse DNS.
- Does forward-confirmed reverse DNS (FCrDNS) match? The PTR hostname should resolve forward back to the same IP. A mismatch looks suspicious.
- Does the PTR hostname look legitimate? Generic, ISP-style reverse names can lower your reputation compared with a proper mail hostname.
Reverse DNS is not a substitute for SPF, DKIM, and DMARC — you need all of them — but missing or mismatched PTR records are a common, avoidable cause of deliverability problems.
How PTR Records Are Delegated
Here is the part that trips people up: you usually cannot set your own PTR record directly the way you set an A record. Reverse DNS for an IP lives in the in-addr.arpa (IPv4) or ip6.arpa (IPv6) zone, and authority over that zone belongs to whoever controls the IP block — typically your hosting provider or whoever assigned you the address.
In practice this means PTR records are set in one of two ways: through a control panel your provider exposes for IPs assigned to you, or by the provider delegating the reverse zone to your own nameservers (common when you have a larger block). If you bring your own IP space (your own allocation), you control the reverse delegation yourself via your RIR.
IPv6 Reverse DNS
IPv6 reverse DNS works the same way conceptually but the zones are far larger, and the nibble-reversed ip6.arpa notation is tedious to write by hand. Many providers and tools generate these for you. If you send mail over IPv6, set the PTR for the specific IPv6 address your mail server uses, because some receivers check it.
Quick Checklist
- Every public-facing server, and especially mail servers, should have a PTR record.
- The PTR hostname should resolve forward to the same IP (FCrDNS).
- Use a meaningful hostname (e.g.,
mail.yourdomain.com), not a generic provider default. - Set PTR for both IPv4 and IPv6 if you serve traffic on both.
How Noded Handles It
We let customers manage reverse DNS for the IPs assigned to their services, and for larger allocations we can delegate the reverse zone to your own nameservers. If you are setting up a mail server and want deliverability right from day one, we can make sure your PTR records and forward-confirmed reverse DNS are configured correctly before you send your first message.
FAQ
Can I set a PTR record myself?
Only if you control the reverse zone for that IP. Usually the IP owner — your hosting provider — sets it, either through a panel they give you or by delegating the reverse zone to your nameservers.
Will missing reverse DNS really send my email to spam?
It can. Many receiving mail servers penalize or reject mail from IPs with no PTR record or with mismatched forward-confirmed reverse DNS. It is one factor among several, but an easy one to get right.
What is forward-confirmed reverse DNS (FCrDNS)?
It means the PTR hostname for an IP resolves forward (via an A/AAAA record) back to that same IP. Matching in both directions is a basic legitimacy signal that many mail servers check.
Do I need PTR records for IPv6?
If you serve traffic — particularly email — over IPv6, yes. Set the PTR for the specific IPv6 address in use, since some receivers check it just as they do for IPv4.