Uses
- Most e-mail mail transfer agents (server software) use a FCrDNS verification and if there is a valid domain name, put it into the "Received:" trace header field.
- Some e-mail mail transfer agents will perform FCrDNS verification on the domain name given on the SMTP HELO and EHLO commands. This can violate RFC 2821 and so e-mail is usually not rejected by default.
- The Sender Policy Framework e-mail anti-forgery system uses a FCrDNS check in its "ptr:" mechanism.
- Some e-mail spam filters use FCrDNS checks as an authentication method for domain names or for whitelisting purposes; for example, according to RFC 5451.
- SpamCop uses the FCrDNS check, which sometimes causes problems for SpamCop users who are also customers of internet service providers who do not provide properly matching DNS and rDNS records for their mail servers.
- Some FTP, Telnet and TCP Wrapper servers will perform FCrDNS checks.
- Some IRC Servers perform FCrDNS checks to prevent abuse.
Read more about this topic: Forward-confirmed Reverse DNS