Question 1

What is reverse DNS (PTR) and why does it matter for email?

Accepted Answer

Reverse DNS maps an IP address to a hostname via a PTR record. For email, this is critical: receiving mail servers perform a PTR lookup on the connecting IP and expect to find a valid hostname (e.g., mail.yourdomain.com). If no PTR record exists, many servers will reject or spam-filter the message.

Question 2

What is FCrDNS?

Accepted Answer

Forward-Confirmed Reverse DNS (FCrDNS) means the PTR record resolves to a hostname that, when resolved forward (A/AAAA lookup), points back to the original IP. This bidirectional consistency is required by strict mail servers (postfix, Sendmail) and is a positive reputation signal for spam filters.

Question 3

How do I set up a PTR record for my mail server?

Accepted Answer

PTR records are controlled by the owner of the IP address range, not the domain owner. For cloud servers (AWS, Azure, GCP, DigitalOcean), set the reverse DNS through your cloud provider's console or API. For on-premise servers with ISP-allocated IPs, contact your ISP to set the PTR record.