_MobileItem.Importance Property
Office 2010
Returns or sets an OlImportance constant that indicates the relative importance level for the MobileItem object. Read/write.
Assembly: Microsoft.Office.Interop.Outlook (in Microsoft.Office.Interop.Outlook.dll)
This property corresponds to the MAPI PidTagImportance Canonical Property property.
The inspector for the MobileItem object does not support assigning an importance level to a MobileItem item. However, you can assign an importance level through the context menu in the user interface for the item, or programmatically by using the Importance property.