Currently, this is not possible since Mendix does not support server push (the server never takes the initiative in contacting a client).
The only work-around i can think of is to poll for messages, using a microflow, when a user enters a common place such as the home (start) form (or, a little more dirty, invokes a common microflow).
Michel, thanks for your feedback. Maybe my question wasn't clear enough, but I really need to know how I can 'push' a message (i.e. an important status update all users that are logged in should know about) to many users at the same time. Anyone any suggestions how to get this working?
Toaster are basically the non blocking version of our client messages.
So in microflow, you throw a client message but uncheck the checkbox in the lower right (blocking true or false)