If you go under Sounds and scroll down to the bottom and you will see Set Ring Tones/Alerts - hit that and on the next menu you will see
+ Messages - hit this and you should see all of your different email accounts, hit the one you want and it will give the options to choose whatever alert you want and other options - just make sure to hit the return arrow - so you will be prompted to save it.
That should take care of it
