How does rDNS affect email authentication?

rDNS interacts with authentication indirectly:

Separate check: rDNS verification happens independently of SPF/DKIM/DMARC. Different evaluation stage.

Pre-authentication gate: Some receivers check rDNS during SMTP connection, before seeing the message. Failed rDNS = connection rejected before authentication can be checked.

Reputation component: rDNS quality feeds into overall sender reputation scores alongside authentication results.

Not sufficient alone: Good rDNS does not replace authentication. Both are required.

Think of rDNS as proving server legitimacy, while SPF/DKIM/DMARC prove message authorization.

Ship registration checked at the harbor entrance. Cargo manifests checked at the dock. Both required.