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.

To force and add-in to always stay enabled, create the following registry value:

KEY: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\Resiliency\AddinList

NAME: ProgID of the add-in

VALUE: 1

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To find the ProgID for an add-in, look in the registry here: HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins HKEY_LOCAL_MACHINE\Software\Microsoft\Office\Outlook\Addins Every subkey of one of the above keys is named with a ProgID of the corresponding add-in.

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These are common Outlook Add-ins ProgIDs, which may need to be forcibly enabled: ESET.OutlookAddin (ESET) Search.OutlookToolbar (Search) UmOutlookAddin.FormRegionAddin (Exchange core)

If you require more detailed technical information, you will find it in this Microsoft article.