There seems to be an issue with the way Microsoft 360 constructs/verifies the DMARC signature.

The following workaround should resolve the issue

In NetCommunity you will need to add a reply email in the add
  1. Go to: Email > Messages
  2. Click the pencil next to the email to edit
  3. Click "More options..."
  4. Enter a Reply address
  5. This can be any email address but we suggest using the "from" address here as well
  6. Save

If you have disabled your DMARC settings, have your IT department re-enable DMARC and test. 

Doing this should allow DMARC to pass in Microsoft 360