Just extracted the .RGU file from his ROM. He has the following value cooked into it:
[HKEY_CURRENT_USER\ControlPanel\Notifications\{A877 D65A-239C-47a7-9304-0D347F580408}]
"Default"="Messaging: New e-mail message"
"Wave"="
\\Windows\\newemail.mp3"
"Options"=dword:00000001
"Duration"=dword:00000000
I have had roms not let me change cooked settings before so this might be the case. They always seem to revert back after a
soft reset. This might be the case for you if your change it and it doesn't stick.