Outlook only exposes that property directly in Outlook 2003. In earlier
versions you would have to use CDO 1.21 or Extended MAPI code. MAPI can only
be programmed using C++ or Delphi, however, not C#.
There is a COM example of getting the actual sender email address using CDO
1.21 code written in VBA/VB6 at http://www.slovaktech.com/code_samples.htm#FromAddress, you can try to
translate that into C# code if you want.