Active X One-Off forms must only be enabled to load with Outlook Controls.

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.

Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Allow Active X One Off Forms is set to "Enabled" "Load only Outlook Controls".

Use the Windows Registry to navigate to the following key:

HKCU\software\policies\microsoft\office\16.0\outlook\security

If the value for allowactivexoneoffforms is REG_DWORD = 0, this is not a finding.

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".