It's unclear whether you want to turn off email notifications or disable email totally. For the latter, go into Settings > Manage apps and tap on email in the "All" listing. Once there, clear cache and clear data, and you will never hear from email again (unless you go into the app and reconfigure it again). If it's just notifications you are trying to eliminate, it's a setting within the app (typically, Menu > Settings and then tap the configured account name and uncheck Email notifications).