In reviewing Message Audit Logs you find that the DMARC results for a message unexpectedly show the status as "none".
This issue can occur when the Messaging Gateway is not able to resolve the DMARC TXT record in DNS.
Correct your DNS settings so the DMARC record can be obtained by the Messaging Gateway. You can use the nslookup tool to verify that the DMARC TXT record can be resolved.