/ Glossary — Infrastructure
What is reverse DNS?
The PTR record that maps a sending IP back to a hostname — and a baseline mail servers check before they trust you. Missing it gets mail rejected. Here's how it works.
/ Definition
Reverse DNS is the lookup that maps an IP address back to a hostname, stored in a PTR record. It's the opposite of normal DNS, which maps a name to an address. For email, it matters because receiving mail servers check the PTR of every connecting IP, and many reject or penalize mail from an IP that has none — a missing PTR is one of the clearest signs of a misconfigured sender.
The stronger check is forward-confirmed reverse DNS (FCrDNS): the PTR points to a hostname, and that hostname's forward record points back to the same IP. Receivers trust FCrDNS far more than a plain PTR, because it proves the sender controls both ends of the mapping. You can check any IP's reverse DNS with our reverse DNS checker.
/ In practice
Why mail servers require it
Legitimate mail infrastructure almost always has reverse DNS set, so its absence is a strong negative signal — which is why several major providers reject mail from an IP with no PTR at the connection level, before authentication is even considered. For any IP you send production email from, a valid PTR is a baseline requirement, not an optional extra. The complication is that reverse DNS is controlled by whoever owns the IP block — your host, cloud, or ISP — not through your own DNS, so setting it often means a request to your provider.
FCrDNS and generic PTRs
Two refinements decide how much your PTR helps. Forward-confirmation — the round trip closing back to your IP — is what receivers actually trust, so a PTR that doesn't forward-confirm carries little weight. And a generic PTR, the default name a host assigns to a pool like 203-0-113-5.pool.example.net, signals shared or dynamic infrastructure rather than deliberate mail sending; many filters treat it with suspicion. For serious sending, you want a PTR that reflects your own mail hostname, which is one of the advantages a dedicated IP gives you.
/ Fixing reverse DNS
Who controls it and how to set it
The thing that trips people up about reverse DNS is that you don't control it through your own DNS. The forward record — your hostname pointing to your IP — lives in your zone, but the PTR lives in the reverse zone for the IP block, which is controlled by whoever owns that block: your host, cloud, or ISP. Setting or fixing a PTR means going to them, not editing your own DNS. On shared infrastructure you may not be able to set it at all, inheriting the provider's generic name. This split is exactly why a dedicated IP matters for reverse DNS: it lets you set a PTR to your own mail hostname and forward-confirm it against DNS you control, giving you a clean round trip a shared pool can't give. None lives in your own zone.
/ Related terms
A clean PTR is the floor. We set it and confirm it.
We run dedicated IPs with self-controlled, forward-confirmed reverse DNS set to your own mail hostname. Bring us your sending setup and we'll check the foundation.
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