Message Received Notification not working

Hey, 
when I am sending a message the "message sent" notification is shown.
But the receiver does not get the "message received" notification.
Is there any chance that I am missing something?

*EDIT*
It seems that the "notification" app has changed its name:
https://pinax-notifications.readthedocs.io/en/latest/

It is now called pinax.notifications

Can you fix this?