A hierarchy of folders in Microsoft Outlook and other Microsoft Windows messaging clients that users can create and modify and that stores users’ messages and attachments. Personal folders, which can be stored on the client machine or on a network share, have the extension .pst.
In many situations, it is advantageous not to use personal folders. Using personal folders can make messages less accessible. For example, Microsoft Exchange Server stores users’ messages in the information store on the Exchange server. This allows users to access their messages from any messaging client that can access the Exchange server. If messages are moved to personal folders, those messages can be read only from clients that can access the personal folders file. It is possible to use a combination approach, in which messages that need to be accessible from different clients can be left on the server and messages that are rarely accessed can be moved to personal folders. Here are some reasons why you might want to use personal folders:
Users can password protect their personal folders, but if they forget the password they cannot reset it.