This article is a good addition to the article 'Add-in keeps disabling'. As a administrator it is possible to enforce the Sendent Outlook add-in to always be enabled. This overrides any user interactions they might have prior with the Outlook add-in and prevents users from ever disabling the add-in.
In the registry navigate to this key:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\Resiliency\AddinList
There you can create a STRING with the name 'SendentOutlook' (no quotes) and give it the value '1'.
In some cases the registry keys 'Resiliency' and/or 'AddinList' do not exist yet, you can create them in that case.