I was confused with g).
Thx for comming.
The statement $\displaystyle \exists x\,\forall y\, (M(x,y)\wedge y\ne x)$ means that there is a student (x) who has emailed everyone in the class and who is different from everyone in the class. But that would mean in particular that x is different from himself/herself. Obviously that's not possible.
You could have given the alternative solution $\displaystyle \exists x\,\forall y\, ((y= x) \vee M(x,y))$ (meaning that either x=y or x has emailed y).