User Configuration > Administrative Templates > Microsoft Outlook 2016 > Outlook Options > Preferences > Junk E-mail
User
HKCU\software\policies\microsoft\office\16.0\outlook\options\mail
By default, when a new Junk E-mail Filter list is deployed, Outlook appends the new Junk Mail Import List to the existing list. Enable this setting to replace the existing list with the new list, instead of appending to the current list.