The Sun Message Store is composed of users. Each user has an Inbox, where new mail arrives, and can have one or more folders or mailboxes, where mail can be stored. A folder can contain other folders in a hierarchical tree.
Folders owned by a user are private folders.
In addition to a user owning a folder, a common user or group can share the ownership of a folder. This type of folder is called a shared folder. A shared folder can be private or public. A notable feature of the Sun Message Store is that it maintains only one copy of each message. This feature enables a single process to manage a large number of connections.