DMARC
Domain-based Message Authentication, Reporting, and Conformance
An email authentication protocol that builds on SPF and DKIM to protect against email spoofing. Proper DMARC configuration is essential for emails sent from Salesforce to be delivered reliably.
Example use case
An IT team configures DMARC DNS records to instruct receiving mail servers to reject emails that fail SPF or DKIM checks for their Salesforce sending domain.