Try this one :
Local cEmail,cSubj
DECLARE INTEGER ShellExecute IN "Shell32.dll" ;
INTEGER hwnd, ;
STRING lpVerb, ;
STRING lpFile, ;
STRING lpParameters, ;
STRING lpDirectory, ;
LONG nShowCmd

cEmail="khan.software@khan.co.nz"
cSubj="Email test from KSL"
=Shellexecute(0,"Open","mailto:&cEmail?subject=&cSubj","","",0)

HTH