Forward Confirmed Reverse DNS (FCrDNS) is a DNS technical configuration that shows a relationship exists between an IP address and a hostname. By having FCrDNS, you prove that your IP address is using a sending domain that you own. This relationship provides a form of authentication that some mailbox providers use in their spam filter methodology.
Requirements for FCrDNS
- The sending IP address must have a valid pointer (PTR) record in DNS which resolves to a valid hostname.
- The hostname must then have an A record in DNS which matches the sending IP address.
- The rDNS (PTR record) for IP address 123.45.678.89 is contact.example.com.
- The A record for contact.example.com is 123.45.678.89.
- The PTR record matches the A record, which means the IP address has FCrDNS.