What is Reverse DNS (rDNS)?

You send an email, and the receiving server wants to know one thing before it even looks at your content: are you who you say you are? Reverse DNS is one of the first checks it runs.

Reverse DNS (rDNS) maps an IP address back to a hostname. It's the opposite direction from regular DNS. Forward DNS takes a hostname like mail.tidalmail.com and resolves it to an IP address (192.0.2.1). Reverse DNS takes that IP address and asks what hostname it points back to.

Forward: mail.tidalmail.com → 192.0.2.1
Reverse: 192.0.2.1 → mail.tidalmail.com

The record that stores this reverse mapping is called a PTR record. It lives in a special DNS zone called in-addr.arpa (for IPv4 addresses). You don't create PTR records in your own DNS panel. They're controlled by whoever owns the IP address, which is usually your hosting provider or ISP.

When a receiving mail server gets your email, it looks up whether your sending IP has a valid PTR record. If it doesn't find one, or if the hostname it finds doesn't match what your server announced, that's a red flag. A lot of spam comes from IP addresses with no rDNS configured at all, so missing rDNS is an easy filter to run.

So this is also why rDNS matters as part of your broader email authentication setup. It works alongside SPF, DKIM, and DMARC, not instead of them. None of those protocols fix a missing PTR record, and a missing PTR record won't be saved by a perfect DMARC policy.

If you're sending from your own IP (not a shared ESP), contact your hosting provider and ask them to create a PTR record pointing your IP to your mail hostname. It's usually a quick support ticket. If you're on a shared sending infrastructure through an ESP like Postmark or Mailgun, they handle rDNS for you on their shared IPs.

Not sure if your sending domain's authentication is all lined up? Our free Email Header Analyzer can show you exactly what receiving servers see when your mail arrives, rDNS included.