Question 1

What is reverse DNS?

Accepted Answer

Reverse DNS (rDNS) is the process of resolving an IP address back to a domain name, using PTR records in the in-addr.arpa zone. While forward DNS goes from domain → IP, reverse DNS goes from IP → domain. It is primarily used for verification, logging, and email delivery.

Question 2

What is a PTR record?

Accepted Answer

A PTR (Pointer) record is the DNS record type used for reverse DNS lookups. It maps an IP address to a hostname. For example, a PTR record for 8.8.8.8 returns dns.google. PTR records are stored in the in-addr.arpa (IPv4) or ip6.arpa (IPv6) zones and are managed by the IP address owner.

Question 3

Why does reverse DNS matter for email?

Accepted Answer

Many email servers check that the sending IP address has a valid PTR record that matches the forward DNS (the domain name resolves back to the same IP). This is called FCrDNS (Forward-Confirmed Reverse DNS). Missing or mismatched PTR records cause emails to be rejected or marked as spam by receiving mail servers.

Question 4

How do I set a PTR record?

Accepted Answer

PTR records must be configured by the organisation that owns the IP address — typically your ISP, hosting provider, or cloud platform. For AWS, use Route 53 in the VPC settings. For GCP, go to VM Instance network interface settings. For dedicated servers, contact your hosting provider's support to set reverse DNS.

Reverse DNS Lookup

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