This Warning indicates that the DMARC record for this domain is not currently protected against phishing and spoofing threats. To resolve this Warning you will need to set a Quarantine or Reject policy on the domain's DMARC record. Setting a Quarantine or Reject value will prevent fraudsters from spoofing the domain as mail servers will Quarantine or Reject messages that fail authentication tests.
*Note: It is advised to not set a Quarantine or Reject policy until you have evaluated your DMARC reports to make sure you don't have any legitimate senders that have email delivery problems.