Right-click an empty area on the Desktop & choose "Personalise".
Click "Sounds" at the bottom of the personalisation box.
Scroll down to "New Mail Notification" and highlight it.
Choose a different sound from the selection bar below.
Preview the sound by clicking "Test"
When you're happy with your new choice, click "Apply"
You may want to "Save" your new scheme with a different name before clicking 'OK'
Your chosen new mail sound will probably be duplicated by some other system event, so you may have to do a bit of trial error to avoid getting misled when you hear it.
Note: You might ask "Why not simply select a different scheme?" to get a different "New Mail" sound, but that has no effect because the default "New Mail" sound is a constant throughout all the schemes.
Edited by phillipcorcoran, 28 May 2010 - 12:46 PM.