The public information store is the primary mechanism used by MAPI clients to gain access to public folders. Although public folders may be located in different information stores, the folder hierarchy independently represents all public folders and subfolders, as shown in the following illustration.
The public folder hierarchy is stored in the information store. The Microsoft Exchange Server service provider uses an index made up of the public folder objects to list the top-level folders to return to the MAPI client. When a MAPI application is used to view the subfolders of a top-level public folder, the provider connects to an information store that maintains an instance of the folder contents. The provider then goes to that information store for all subsequent contents operations in that folder.
Any changes to the public folder hierarchy are performed by the user's hierarchy server. Content tables and messages are provided by the folder content servers.