Using public folders on a Microsoft Exchange Server computer can have a dramatic effect on the server's performance. Size, frequency of user access, various views on that folder, the number of replicas, the replication schedule, and how often its content changes are all factors that affect server performance. If many users frequently use a public folder, the server is going to be kept busy satisfying those requests. The public folder also keeps track of the expansion state of each folder and the read/unread state of each message on a per-user basis.
Although public folder replication is a rapid process, changes to a public folder are replicated according to a schedule set up by the administrator. Even if the replication schedule is set to Always, replication occurs only every 15 minutes. If replication starts when a user is accessing a public folder or the public folder hierarchy, the user will notice a sudden slowdown that improves only after the replication process is completed. If there are a number of public folder replicas to update, this places even more stress on the server and extends the replication process.
Public folders can contain messages and free-standing documents. Messages are like any other mail message in terms of the resources they consume on a server. Free-standing documents, however, are another performance issue because they are frequently large documents. For example, whenever a user opens a 1 MB file in a public folder, 1 MB of data must travel across the network. This affects the performance of the server for every user.