As proposed by Hans Verduyckt in Exchange Online Virtual team meeting 12/03/2019:
Proposed change: set standard OwaMailboxPolicy value OutlookBetaToggleEnabled to False so users can not use "outlook preview"
Thomas Jadot & Didier Van Reeth approved this proposal with the following remarks:
- change the "OwaMailboxPolicy-Default" value OutlookBetaToggleEnabled to False
- create extra "OwaMailboxPolicy-test" with this option available for test purposes
status: tested OK - to be planned
DONE 18/03/2019