In 2.3.6, I was able to control the notification volume independently in the Sound settings. Useful on days you wanted to shut notifications up but still hear incoming calls. Additionally I can't seem to set the notification sound for Email. If I go to Personalize -> Sounds, I can see the ringtone, system wide notification and alarm settings. Clicking the Sound Set lists the Mail sound but does not allow you to change any of them from here. Message's ability to change the sound is still in the app itself as well as the Calendar's. Mail seems to be the only app allowing you to turn it on/off but not choose it's sound.