_Explorer.Selection property

Returns a Selection object consisting of one or more items selected in the current view. Read-only.

Namespace:  Microsoft.Office.Interop.Outlook
Assembly:  Microsoft.Office.Interop.Outlook (in Microsoft.Office.Interop.Outlook.dll)

Selection Selection { get; }

If the current folder is a file-system folder, or if Microsoft Outlook Today or any folder with a Web view is currently displayed, this property returns an empty collection. Also if a group header is selected, the Count property on the selection returns zero.