Problem light through walls

Hello all

i'm very new to unity5 and while i started to get in touch with some features. I know this problem i have right now is not new. But i could not find any solution for that.

Simpy a spotlight is set near the wall. The facing wall behaves correctly and the shadow is casted well. My options were : soft shadow cast in the light options. Sadly the back of the wall receives also the spotlight, what is quite not correct. So what am i doing wrong here ? See below for settings. All Objects are connected to mesh colliders

Thanks for any help