To ensure that emails sent from SecurityGateway to Microsoft Office 365 as a result of its pre-filtering process are not incorrectly treated negatively or labelled as spam we would recommend that you add the SecurityGateway public IP address to Microsoft’s Office 365’s Enhanced Filtering.
It’s initially necessary to ensure you have a suitable Inbound (Receive) connector configured in Microsoft Office 365:
You must now configure an Enhanced Filter for this Inbound (Receive) connector in Microsoft Office 365:
This Microsoft document also describes the use and configuration of Microsoft’s Office 365’s Enhanced Filtering.