This has got to be one of the most enjoying features that is enable by default on many new Android phones, these alerts wake you up in the middle of the night with announcements like “1 new emails” even when the phone is set to silent or vibrate.
Luckily there is a solution to stop the digitized text to speech voice without stopping new emails from coming in.
Go to Settings>Voice input and output>Text-to-speech settings and uncheck Driving mode
After doing this you shouldn’t hear these awful notifications, while still receiving email as per normal.
Screenshots below show the procedure done on Android 2.3.5