Hi Raymond,
The problem is that the Excel file needs to be sent via mail from ABAP.
The only way I've found is by using the 'cl_bcs' class or the 'SO_*_API1' FMs. In both cases the data is structured in ABAP so that it can be read by Excel and the extension is passed to either the method or the FM.
Best Regards,
Niels De Greef