I use the announcement tool to communicate to all students in a course. It goes to them via their notification setting which is defaulted to their email. Since I believe most students don't change this, I think it's a good solution. And if they do change it, it was deliberate and they are probably more aware of the notifications than those who don't.
Also, I have the setting turned on to post recent announcements on the home page, so student can view it there as well. So they have two opportunities to view the information.
At the beginning of the course I make them aware of how I will communicate with them, it's their responsibility to stay up on it. (I teach in Higher Ed.)
I use the Inbox to message students individually.
This discussion post is outdated and has been archived. Please use the Community question forums and official documentation for the most current and accurate information.