You can share sub-folders that are created in the Mailbox and Home folders.
To share a folder:
Right-click the folder that you want to share and select Sharing.
Type in the names of the people you want to share the folder with and select them as they auto-fill.
Select which permissions you want to grant to each individual (Add, Edit, Delete), and then click Save.
Users are sent a message saying you shared a folder with them. If you are shared a folder, you can accept the share in the notification message.