User Configuration > Administrative Templates > Microsoft Outlook 2016 > Security > Security Form Settings > Attachment Security
User
HKCU\software\policies\microsoft\office\16.0\outlook\security
By default, OLE package objects are not displayed in e-mail messages. You can change this behavior so that the package appears in the body of the e-mail message as an icon that represents an embedded or linked OLE object. When users double-click the icon representing the package, the program used to create the object either plays the object or opens and displays it. Be aware that the icon for OLE package objects can be easily changed and used to disguise malicious files. To set Exchange Security Form settings by using Group Policy, note that this policy setting only applies if the "Outlook Security Mode" policy setting under "Microsoft Outlook 2016\Security\Security Form Settings" is configured to "Use Outlook Security Group Policy."