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 had set your DMARC policy to 'none', have your IT department re-enable and test.
Taking this step will allow DKIM to verify and allow DMARC to pass in Office 365