If you have the Send broadcast private messages permission (see Permission descriptions), you can send a broadcast message. These messages are delivered as announcements, and those who receive one ...
@alodiac In Aurora, members of a community cannot turn off their private messages (and there are no plans to allow this in the future), so they will always receive broadcast messages!
...... Why? I have employees who can not deal with the spam they receive, and similarly users who absolutely do not want to get notified. Why in the world would this be smart to remove the only protection they have? This is a horrible idea.