There are two parts to public folders:
Public folder hierarchy The structure of the public folders as they are displayed in Microsoft Outlook or the Microsoft Exchange Server Administrator program.
Public folder content The information contained in the public folder.
During public folder replication, the hierarchy is replicated to every public folder server, but the content is replicated only to servers where replicas have been set up by an administrator. When a user creates a public folder, its location in the hierarchy is replicated to every public folder server. If the new public folder is a top-level public folder, the contents of the new folder are on the user's public folder server (as specified in the General property page of the user's private information store). If the new public folder is not a top-level public folder, the contents are located on every public folder server where the parent's contents reside.
During replication, changes made to items in a replica are sent to all other replicas of the public folder throughout the organization. Changes made to the folder, a folder's properties, or the public folder hierarchy are replicated to all public folder servers (even those without replicas of this folder). When you no longer want a specific public folder replica, you can delete it from its information store.
When more than one replica of a public folder exists, connections users make are distributed across all replicas in a site. If there is a replica of the public folder on the user's public folder server, the first attempted connection will be to that replica. If the replica cannot be connected to because a server is down or a network connection cannot be made, a connection to a different replica in that site is attempted. Each replica in the site is attempted in turn. If none can be connected to in the site and public folder affinities are set up, connections to replicas in different sites are attempted. For information about setting up public folder affinity, see Chapter 8, "Setting Up Server Core Components and Properties."