Caches certain properties for extremely fast access to those particular properties of an item within the collection.
Assembly: Microsoft.Office.Interop.Outlook (in Microsoft.Office.Interop.Outlook.dll)
The SetColumns method is useful for iterating through the Items object. If you don't use this method, Microsoft Outlook must open each item to access the property. With the SetColumns method, Outlook only checks the properties that you have cached. Properties which are not cached are returned empty.