User Configuration > Administrative Templates > Microsoft Outlook 2016 > Account Settings > Exchange
User
HKCU\software\policies\microsoft\office\16.0\outlook\options\folders
This policy setting prevents users from changing their mail folder permissions. If you enable this policy setting, Outlook users cannot change permissions on folders; the settings on the Permissions tab are disabled. Enabling this policy setting does not affect existing permissions, and users can still change permissions by sending a sharing message. If you disable or do not configure this policy setting, Outlook users can change the permissions for folders under their control by using the Permissions tab of the Properties dialog box for the folder.