no DMARC on nextdns.io

While I certainly agree that DMARC is helpful to prevent domain spoofing, it only affects email traffic and nothing else. DMARC helps to tell other email systems what should be done if a message fails SPF and DKIM checks.

But as most major email services have filters that include checking SPF and DKIM compliance on their own (which is done even if there isn't a DMARC policy), DMARC is certainly not a required piece of the Email/DNS puzzle. It simply allows a domain owner to specify that messages appearing to be from their domain failing those checks should be rejected, quarantined, or allowed through.