DMARC
The policy that tells the world's mail servers what to do with email that fails SPF and DKIM.
What this means: without DMARC, there is no instruction telling mail servers to block spoofed email claiming to be from yourcompany.com, even if SPF and DKIM are perfect.
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No DMARC record found at _dmarc.yourcompany.com.
How to fix it: publish a TXT record at
_dmarc.yourcompany.comcontainingv=DMARC1; p=none; rua=mailto:you@yourcompany.com, read the reports for a few weeks, then tighten the policy top=reject.