Understanding DMARC Policies and Its Independence from SPF Qualifiers

SPF (Sender Policy Framework) is an email authentication protocol that helps prevent email spoofing by verifying the sending server’s identity and determining if it’s authorized to send emails on behalf of a specific domain.

  • What are SPF qualifiers?

SPF (Sender Policy Framework) uses qualifiers to define the result of the SPF check performed by the receiving mail server. These qualifiers indicate whether the SPF check has passed, failed, or encountered a soft fail.

Pass (+): Indicates that the SPF check has successfully matched the sending server’s IP address with the authorized list in the DNS SPF record. The email is considered authentic.

Fail (-): Indicates that the SPF check has failed, meaning the sending server’s IP address is not listed in the authorized SPF record. The email is treated as potentially unauthorized or spoofed.

Soft Fail (~): Represents a less strict result than a fail. A soft fail indicates that the SPF check did not produce a definitive failure, but the receiving server should treat the email with caution. It’s a way to indicate a less strict policy without outright rejecting the email.

Neutral (?): Represents a result where the SPF record for the domain does not explicitly indicate whether the server is authorized or not. It neither passes nor fails the SPF check.

DMARC (Domain-based Message Authentication, Reporting, and Conformance) policies work by allowing domain owners to specify how receiving mail servers should handle emails that fail authentication checks, providing a framework to combat phishing attacks and unauthorized use of their domains.

  • How DMARC policies work:

none: In the monitoring phase, the “none” policy is often used. It allows domain owners to receive reports on email authentication results without taking immediate action on failed emails.

quarantine: The “quarantine” policy directs receiving mail servers to place failed-authentication emails in the recipient’s spam or quarantine folder.

reject: The most stringent policy, “reject,” instructs mail servers to outright reject emails that fail DMARC authentication.

  • SPF Qualifiers in the Presence of DMARC:

Since the SPF qualifiers “Softfail” and “Hardfail” are essentially the same as the DMARC qualifiers “quarantine” and “reject,” the handling of an email by the receiving mail server is determined by the DMARC policy rather than the qualifiers. When DMARC is implemented, the SPF qualifier interacts with the DMARC policy to determine the fate of an email that fails SPF validation. The DMARC “p” tag takes precedence over the SPF qualifier and dictates the recipient’s mail server’s action.

For example, if the SPF qualifier is “-” (Fail), but the DMARC “p” tag is set to “quarantine,” the recipient’s mail server will likely quarantine the email instead of outright rejecting it. Similarly, if the DMARC “p” tag is set to “reject,” the email will be rejected, irrespective of the SPF qualifier.

Because of its independence, DMARC can function as a stand-alone authentication protocol and make intelligent judgments based on policy and alignment.

In conclusion,

DMARC is like a strong shield against phishing attacks. It works on its own without relying on SPF qualifiers. With its alignment checks, strong policies, and helpful reports, DMARC is a powerful tool in the battle against cyber threats. It’s important for organizations to know that DMARC works independently from SPF qualifiers to create a complete and successful email security plan.