InformationBy 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. The recommended state for this setting is: Enabled:Load only Outlook Controls.
If additional types of Active X controls are allowed, particularly un-trusted third-party controls, the risk of malware infecting the computer increases.
SolutionTo implement the recommended configuration state, set the following Group Policy setting to Enabled.
User Configuration\Administrative Templates\Microsoft Outlook 2016\Security\Allow Active X One Off Forms
Then set the Allow Active X One Off Forms option to Load only Outlook Controls.
This setting enforces the default configuration and therefore should not have any effect on usability.