So in response to this I did some testing and wanted to let you all know that ToddM's post was correct that this will indeed fix the OP post about the issue, however there is a caveat to this in which i found that it works with this.
Mail notifications in general are contained by default in the Settings-Sounds-Mail changing here will change them if you have only one account. IF you have multiple changing here will not alter the settings as intended. This is how i found and successfully was able to change and validated that it's working. Brand New Iphone 5 OS 6.0.2 or whatever update is on it now. Sprint btw.
Settings -> Notifications -> Mail Accounts if you have more than one -> Like i have Exchange and iCloud. Click on either one scroll down, you will see New Mail Sound. Change this here and then test. I did this 4 x for each account with out changing the default one. I had the default set to Tweet, and then changed the other 2 under notifications to custom, none, and TriTones and alternated and its working perfectly.
Just some food for thought.