Download dll files
You can put them anywhere you like, preferable a path you can type easily. In below example i've put them under d:\MSGPreviewer
You also need .NET 4.5 , a newer version is good too.
Now you need to run Command line in administrator mode. You can do this by create a shortcut to cmd.exe and right mouse click and choose run as administrator.
Goto the directory: C:\Windows\Microsoft.NET\Framework64\v4.0.30319 , by typing: cd C:\Windows\Microsoft.NET\Framework64\v4.0.30319
the type there two commands:
regasm /tlb d:\MSGPreviewer\SharpShell.dll
regasm /codebase d:\MSGPreviewer\msgpreview.dll
This will register the dll files as com object and the previewer should work now.