Support for Custom Property Pages
You can create your own property pages to customize the Properties dialog box for all folders.
A custom property page is an ActiveX control stored in a dynamic-link library (DLL) that implements the PropertyPage object and that’s installed as a COM add-in . This object provides the interface through which Outlook can query the property page about its status and inform the property page that the user has clicked the Apply or OK button.
For more information about property pages, see adding custom property pages.
Customizing the Outlook Options dialog box (available through the Microsoft Office Backstage view) by using property pages has been deprecated. However, you can customize your own tab on the Backstage view using Microsoft Office Fluent user interface extensibility. For more information, see Extending the User Interface in Outlook 2010.