The three policies
p=none— monitor. Mail still delivers; you collect reports.p=quarantine— treat failures as spam.p=reject— refuse failures. The goal for any domain that cares about spoofing.
Look for rua= (aggregate XML reports) and optionally ruf= (forensic). pct= less than 100 means a staged rollout. Alignment tags aspf and adkim default to relaxed. Full walkthrough: DMARC explained. Build a record: DMARC generator.