O365-CO-000014 - Add-on Management must be enabled for all Office 365 ProPlus programs - outlook.exe
Internet Explorer add-ons are pieces of code, run in Internet Explorer, to provide additional functionality. Rogue add-ons may contain viruses or other malicious code. Disabling or not configuring this setting could allow malicious code or users to become active on user computers or the network. For example, a malicious user can monitor and then use keystrokes that user's type into Internet Explorer. Even legitimate add-ons may demand resources, compromising the performance of Internet Explorer and the operating systems for user computers.
Set the policy value for Computer Configuration >> Administrative Templates >> Microsoft Office 2016 (Machine) >> Security Settings >> IE Security 'Add-on Management' to 'Enabled' and select the check boxes for all installed Office programs.