A systems administrator needs to address risks associated with corporate brand impersonation via email. The systems administrator wants a method that permits recipient servers to validate the source…

SPF (Sender Policy Framework) allows a domain owner to specify which mail servers are authorized to send email on behalf of their domain, primarily checking the envelope sender, but doesn't verify the email content or the 'From' header often used in impersonation.

DKIM (DomainKeys Identified Mail) provides a way for an organization to cryptographically sign outgoing email messages, allowing recipient servers to verify that the email was sent by an authorized sender for that domain and that the message content has not been tampered with in transit. This directly addresses source authenticity and brand impersonation.

S/MIME (Secure/Multipurpose Internet Mail Extensions) provides cryptographic security services, such as authentication and integrity for individual email messages, but it operates on a user-to-user basis rather than a domain-wide source authenticity check for brand impersonation.

DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds upon SPF and DKIM to instruct recipient mail servers how to handle emails that fail authentication checks, but it relies on SPF and DKIM for the actual authentication mechanisms.