When a new message is created in a public folder, the information store assigns a change counter number to the message and then sends a replication message to all other information stores that contain instances of the public folder. Information stores that receive the replication message create the message in their replica of the public folder, using the change number assigned by the information store on which the message was created.
When a message is deleted, the information store from which the message is deleted sends a replication message to all other information stores that contain instances of the public folder. This message indicates that the message has been deleted. Each information store that receives the message deletes the message and maintains a marker, called a tombstone, for the deleted message.