Hello @DarkCorner,
Keep it simple:
_dmarc.domain.tld
v=DMARC1; p=reject; rua=mailto:dmarc@domain.tld
A best practice is to collect DMARC emails with a dedicated email account so you can review them to see if there are any issues.
When you are working email delivery, also check if your server’s IP address is not blacklisted:
https://mxtoolbox.com/blacklists.aspx
Sometimes a provider can assign an IP that was used to send spam. If this happens, request a new IP address and check if it is safe.
I hope this helps.
Yours sincerely,
Mantas