User Configuration > Administrative Templates > Microsoft Outlook 2016 > Outlook Options > Mail > Compose Messages
User
HKCU\software\policies\microsoft\office\outlook\addins\umoutlookaddin.formregionaddin
This policy setting controls whether the Outlook Protection Rules add-in is enabled. If you enable or do not configure this policy setting the add-in automatically downloads Outlook Protection Rules from Exchange and processes them when each Exchange mailbox user composes a new e-mail. If you disable this policy setting the add-in does not download or process Outlook Protection Rules.