About the DMARC Checker
The DMARC Checker fetches the policy at _dmarc.yourdomain and decodes every tag: the enforcement level (p=), subdomain policy, reporting addresses and alignment modes. DMARC builds on SPF and DKIM — together they are the standard defense against email spoofing of your domain.
none = monitor only (reports, no action), quarantine = failing mail goes to spam, reject = failing mail is refused outright. Mature setups end at reject.
rua receives daily aggregate XML reports about who sends as your domain — set it (any mailbox or a DMARC service) before tightening the policy, so you see what would break.
No — DMARC evaluates SPF/DKIM results plus alignment with the From domain. Deploy at least one of the two (ideally both) first.