Home/ Glossary/ Reverse DNS

Reverse DNS (rDNS)

Security Glossary - DNS

Definition: Reverse DNS maps an IP address back to a hostname, the opposite of a standard (forward) DNS lookup. Reverse DNS uses PTR records stored in the in-addr.arpa zone for IPv4 or ip6.arpa zone for IPv6. It is primarily used for email server verification and network diagnostics.

The Importance of rDNS

Reverse DNS is critical for email deliverability. Most mail servers perform a reverse DNS lookup on incoming SMTP connections and may reject or penalize email from IPs without valid reverse DNS. A properly configured reverse DNS entry that matches the sending server's hostname (forward-confirmed reverse DNS) signals that the server is legitimate.

Beyond email, reverse DNS is useful for security logging and network diagnostics. When reviewing server logs, IP addresses with reverse DNS entries are easier to identify than bare IP addresses. Network monitoring tools use reverse DNS to associate traffic with hostnames.

Setting up reverse DNS requires coordination with your IP address provider (hosting company or ISP), since PTR records are managed in the IP block owner's zone, not your domain's zone. This is a common point of confusion - you cannot configure reverse DNS through your regular DNS provider.

Testing Your Configuration

A DNS health checker performs reverse DNS lookups on your server's IP addresses and verifies they match your domain (forward-confirmed reverse DNS). If reverse DNS is missing or mismatched, contact your hosting provider to configure PTR records.

Check DNS Health

rDNS FAQ

Why does my email get marked as spam?
Missing or misconfigured reverse DNS is one common cause. Mail servers check that your sending IP has a PTR record matching your sending domain, and that the domain resolves back to the same IP (FCrDNS). Other factors include SPF, DKIM, DMARC, and content quality.
How do I set up reverse DNS?
Contact your hosting provider or ISP - they manage the PTR records for their IP address ranges. Most cloud providers (AWS, DigitalOcean, Vultr) have a reverse DNS configuration option in their control panel. You typically set the PTR to match your mail server's hostname.

Related Concepts

PTR Record (Pointer Record) Domain Name System A Record (Address Record) Email Deliverability MX Record (Mail Exchange Record)
Disclaimer: DomainOptic provides automated informational scans only. Results do not constitute professional security advice, compliance certification, or a guarantee of security. Always verify findings independently.