All users in Moodle may send and receive private messages via Moodle. This is in addition to receiving notifications about assignments, forum discussions etc.
New messages are highlighted with a number in the messaging menu at the top right corner of the screen.
The number indicates the number of people that have sent messages, and not the actual number of messages received.
By clicking on the notification icon, you will see the new messages together with the option to send a new message.
To view all your messages, you can also click on the drop-down menu next to your profile name (top right corner), and select Messages.
A teacher can send a message to course participants as follows: