The following workaround should resolve the issue
In NetCommunity you will need to add a reply email in the add
- Go to: Email > Messages
- Click the pencil next to the email to edit
- Click "More options..."
- screenshot: https://www.screencast.com/t/lNLgp0AFl7bp
- Enter a Reply address
- screenshot: https://www.screencast.com/t/DKO1YBI1b
- This can be any email address but we suggest using the "from" address here as well
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