I think somehow you have to signal that clipboard wants RTF ( RegisterClipboardFormat CF_RTF "Rich Text Format" ), then you have to "selectall" (create selection object, set the range), then copy into clipboard ($message->Copy )

I'm not sure of the exact syntaxt as I couldn't find a direct example, good luck

Clipboard: Using the OLE Clipboard Mechanism (MFC)

Data Objects and Data Sources (OLE)

Chapter 17: Working with Item Bodies in Outlook 2007