This applies to the Outlook desktop application only.
If you use third party Add-ins and/or you find that core Add-ins keep getting disabled as an unwanted behaviour, it is possible to set specific Add-ins to be always enabled. To control an Add-in, create a registry key here:
HKEY_CURRENT_USER\\Software\\Policies\\Microsoft\\Office\\16.0\\Outlook\\Resiliency\\AddinList
Use the Add-in’s ProgID as the string and following values apply:
0 = always disabled (blocked) 1 = always enabled 2 = configurable by the user and not blocked by the Block all unmanaged add-ins policy setting when enabled
To find an Add-in’s ProgID, look here (note that ProgIDs are case sensitive):
HKEY_CURRENT_USER\\SOFTWARE\\Microsoft\\Office\\Outlook\\Addins
These are common Outlook Add-ins ProgIDs, which may need to be forcibly enabled: ESET.OutlookAddin (ESET) Search.OutlookToolbar (Search) UmOutlookAddin.FormRegionAddin (Exchange core)