There seems to be an issue with the way Microsoft Office 365 constructs/verifies the DKIM 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 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