Which method checks to define rules for handling messages in messaging services?

DMARC, which stands for Domain-based Message Authentication, Reporting, and Conformance, is designed specifically to define rules for handling messages in email services. It builds upon the existing standards of SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail), enabling domain owners to specify how incoming mail servers should handle messages that fail authentication checks.

With DMARC, domain owners can publish policies in their DNS records that instruct recipient mail servers on how to manage email that claims to be from their domain but does not pass the SPF or DKIM checks. This includes actions such as rejecting, quarantining, or allowing the message to be delivered normally. By implementing these rules, DMARC helps to reduce email spoofing, phishing attacks, and improves overall email deliverability.

Other options serve different purposes; for example, SMTP (Simple Mail Transfer Protocol) is used for sending emails but does not define rules for handling messages based on authentication status. VPN (Virtual Private Network) provides secure connections over the internet but has no relevance to email message handling. SPF validates the sending mail server's IP address but lacks the policy enforcement capabilities of DMARC, making DMARC the most suitable choice for defining message handling rules in email services.