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What is FCrDNS and what are the requirements?

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.

Example

  • The rDNS (PTR record) for IP address 192.28.144.45 is contact.returnpath.com.
  • The A record for contact.returnpath.com is 192.28.144.45.
  • The PTR record matches the A record, which means the IP address has FCrDNS.
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