To create a replica of an existing public folder, you must have public folder administrator authority. In the Administrator program, either add the new information store to the Instances property page of the public folder or add the public folder to the Replicas property page of the public information store.
When an information store detects a new replica and determines that it is responsible for that replica, it generates a backfill request for the contents of the folder (the folder content packet).
If an information store receives a folder content packet for a folder that does not exist in the hierarchy or for which it does not currently have a replica, it queues the content packet and waits for the folder hierarchy change. It then processes the content packet. If the hierarchy change does not occur within four hours, the packet expires and will have to be backfilled.