Private: Here you can write a private message to parents or an employee - only those who are a recipient can see the message. You must specifically select the name of the recipient so that there is a green cross next to the name.
Team: This inbox allows you to communicate with a room. These messages can be read by all employees who have marked the room as a favourite by starring it. You also have the option to upload photos, attach documents and add videos to a message.
All: Those who have permission to send messages directly to parents also have this inbox, here you can see all the rooms, even those that are not marked as favourite.
Regarding permissions, if employees have the permissions for "Send messages directly to parents (not via team)" then employees can send private messages to parents - as well as parents directly to employees, without other employees seeing the message.
If employees do not have the permission to directly message parents ticked off they can only send messages from team inbox, which other employees in that room can also see.
A parent's view of their inbox can look something like this:
Here they'll have the option to message their child's room as displayed as the first option (Employees in Bella's class).
Parents can also send messages to Management. This can be for administrative and private concerns that they'd rather not share in a group message.
*Note: There is no way to stop parents from having this option.