User Configuration > Administrative Templates > Microsoft Outlook 2016 > Miscellaneous > PST Settings
User
HKCU\software\policies\microsoft\office\16.0\outlook
This policy setting allows you to specify a different folder location for Outlook Data File (OST) files on user computers. If you enable this policy setting, you can specify a location for OST files on user computers. If you disable or do not configure this policy setting, OST files are located in: %LOCALAPPDATA%\Microsoft\Outlook on user computers.