Email authentication
DMARC
Definition
Policy layer that enforces SPF/DKIM results (reject/quarantine) and reports.
For executives (CEO·CISO)
The most effective single step against domain spoofing, and increasingly a de-facto requirement for sending/partnering. Commonly missed: most stay at p=none (monitor) and block nothing — use the reports to fix legitimate senders, then move to quarantine→reject.