Microsoft suggests that tenants wanting to block access to OWA while allowing people to use the new Outlook should deploy a conditional access policy. That’s good advice if a tenant has the necessary Entra P1 licenses and is willing to accept the loss of browser access to Teams. Microsoft 365 is a complicated interconnected place, and blocking one app can have consequences for another…| Office 365 for IT Pros
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.| Office 365 for IT Pros