I have used MFCMapi for a long time and it is a extreamly usefull tool when troubleshooting MAPI issues. If you have not seen, used or heard of it before, I highly suggest that you download a copy and test it out. This is the newest release and contains a lot of new features.
Since this tool has been officially released, MFCMapi will now be known as the Microsoft Exchange Server MAPI Editor. Just so you don't get confused when you download and extract the tool, the binary is still called MFCMAPI.exe.
For more information on all of the new features, please check out Stephen Griffin's blog: http://blogs.msdn.com/stephen_griffin/archive/2006/06/07/621138.aspx