While in Microsoft Exchange Server, the messages, calendar, and other items are delivered to and stored on the server. In standalone applications (Microsoft Outlook, for example), the messages, calendar, and other items are delivered to and stored locally in a Personal Folders (.pst) file that is located on the computer.
Starting with Microsoft Outlook 97 the Personal Storage file is encoded in ANSI format. It has a maximum file size of 2 GB. If the file exceeds this size it will become corrupted. This format is supported by Microsoft Outlook 97, Outlook 98, Outlook 2000, Outlook 2002, and Outlook 2003 Internet Message Access Protocol Version 4rev1 (IMAP4) accounts and HTTP accounts.http://support.microsoft.com/kb/830336
Outlook 2003
Starting with Outlook 2003 the Personal Storage file is encoded in unicode format. It allows a user-definable maximum file size up to 33TB that exceeds the previous limit of 2GB. This format is supported by Microsoft Outlook 2003 and Outlook 2007.[1][2].