Possibly in Outlook 2010, I haven't checked out all the new context menu
stuff there. Not in any earlier versions of Outlook. In Outlook 2007 you can
get the context menu for a right-click on one or more items, but not for the
reading pane.
Using a hack you can get any right-click menu using
Explorer.CommandBars.OnUpdate(), but that doesn't tell you what was clicked
or where and gives you no context.