The ConditionalAccessPolicy setting in an OWA mailbox policy can be configured to work with Entra ID conditional access so that OWA blocks access to attachments on unmanaged devices. Microsoft originally introduced the feature in 2018 and as it turns out, the combination of OWA mailbox policy and CA policy also blocks attachment access for the new Outlook for Windows client.
Recent developments sees the ability to stop Teams users updating their photos by enforcing controls in OWA mailbox policies. Organizers can stop Teams meetings without waiting for everyone to leave with a new End meeting option in the meeting menu. Both changes are rolling out.
Microsoft has announced that the AdditionalStorageProvidersAvailable setting in OWA mailbox policies will now control access to both first-party and third-party storage providers. The new setting is now available and becomes active in August. Before then, you might want to adjust some of your OWA mailbox policies.