TL;DR: Reverse DNS (rDNS) does the opposite of normal DNS — it maps an IP address back to a hostname using a PTR record. Mail servers check the PTR of your sending IP, and if it's missing or a generic ISP-assigned name, they often treat your email as spam or reject it. It's set by whoever owns the IP (your host/ISP), not in your normal DNS. Scan your domain free to check your email foundation.
Forward vs reverse DNS
Normal ("forward") DNS turns yourdomain.com into an IP. Reverse DNS goes the other way:
given 203.0.113.10, what hostname does it claim to be? That answer is a PTR record, published
in a special reverse zone by the owner of the IP block.
Why email cares about it
To fight spam, receiving mail servers check the sending IP's PTR — and ideally that it matches forward DNS (this is called Forward-Confirmed reverse DNS, or FCrDNS). Red flags that hurt deliverability:
- No PTR record at all — looks like a misconfigured or throwaway sender.
- Generic PTR like
host-203-0-113-10.isp.net— typical of residential/dynamic IPs that shouldn't be sending bulk mail. - Mismatch — the PTR hostname doesn't resolve back to the same IP.
Who sets reverse DNS?
This trips people up: PTR records aren't set in your normal DNS host. They're controlled by whoever owns the IP — your hosting provider, mail provider or ISP. If you run your own mail server, ask your host to set a proper PTR that matches your mail hostname.
How to check and fix it
- Look up the PTR of your sending IP (an online rDNS/PTR checker, or
dig -x <ip>). - Confirm it's a real hostname (e.g.
mail.yourdomain.com), not a generic ISP name. - Check it matches forward DNS — the hostname should resolve back to that same IP.
- If it's wrong or missing, ask your host/ISP to set it. (Most people who send via Google/Microsoft don't need to — the provider handles it.)
FAQ
Do I need a PTR record if I use Gmail/Microsoft 365?
No — your provider's sending IPs already have correct rDNS. PTR matters when you send from your own server/IP.
Can I set a PTR in my normal DNS?
No — it lives in the reverse zone owned by the IP holder. You request it from your host or ISP.
Is missing rDNS a guaranteed spam folder?
Not guaranteed, but it's a strong negative signal that, combined with weak authentication, often means rejection.
Sending from your own server and landing in spam? Scan your domain, then reply to your report — we're developers and we'll check your rDNS and authentication and help get it right.