>Generically, the dispatch for the mailto: is handled through the registry; there should be a key HKEY_CLASSES_ROOT\mailto\shell\open\comand; the value of that registry key points to the default mail handler invoked by the operating system for mailto.
>

But different mail reader take different command line switches. Outlook express takes "/mailurl", but I know that others are different. IOW< you can't just switch the location of the program.