Information
Active X One-Off forms must only be enabled to load with Outlook Controls.
GROUP ID: V-223352
RULE ID: SV-223352r961092
By default, third-party ActiveX controls are not allowed to run in one-off forms in Outlook. You can change this behavior so that Safe Controls (Microsoft Forms 2.0 controls and the Outlook Recipient and Body controls) are allowed in one-off forms, or so that all ActiveX controls are allowed to run.
Solution
Set the policy value for
User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Allow Active X One Off Forms to 'Enabled'
'Load only Outlook Controls'.