HonorDmarcPolicy in ExchangeOnline vanished from GUI
Did you notice the "Honor DMARC Policy" in the Microsoft 365 Defender AntiPhishing Policy?
A few weeks ago there was a Setting in the GUI but that has been vanisched there. The Setting is still available with PowerShell.
As you can imagine, i was very surprised that this Setting is no longer in the GUI
A few Weeks ago, there was this Setting in the Policy
Now it's only available in PowerShell
Get-AntiPhishPolicy | ft name
Get-AntiPhishPolicy -Identity "Icewolf Anti Phishing" | fl *dmarc*
Microsoft has a good Flow Diagram where it explains SPF, DKIM and DMARC and how they are checked in Exchange Online.
Use DMARC to validate email
To verify i use the Message Header Analyzer https://mha.azurewebsites.net/ and check the "Authentication-Results" Header
There is a good explanan how to interpret these Headers here
Anti-spam message headers in Microsoft 365