No. I have not noticed before. I certainly get an underline for mistakes such as you "teh" and so on. If I then right click it gives me the alternatives. "i" would be a grammar correction, which is , unfortunately not one of the functions of the Email program (It certainly should be).
I am the world's worst typer, and what I do, and the reason I have not picked up on this, is type my messages in Word and then copy and paste. At the moment, it seems that is the only choice, or find an Email program that will do what you require.
I am querying the problem on Microsoft,s Technet pages - it might start the ball rolling.