http://support.microsoft.com/kb/832925 Microsoft Outlook 2013, Microsoft Outlook 2010, Microsoft Office Outlook 2007, and Microsoft Office Outlook 2003 support American National Standards Institute (ANSI) and UNICODE personal folders (.pst) and offline folder (.ost) files. This article describes how to use the following four registry entries to limit the size of both the .pst and the .ost files: The MaxFileSize registry entry The WarnFileSize registry entry The MaxLargeFileSize registry entry The WarnLargeFileSize registry entry Note The WarnLargeFileSize and WarnFileSize registry entries do not enable Outlook to warn you before the file size limit is reached. The MaxFileSize registry entry The MaxFileSize registry entry determines the absolute maximum size that both the .pst and the .ost files can grow to. After this maximum size is reached, Outlook does not permit the size of the file to grow beyond this size. The WarnFileSize registry entry The WarnFileSize regist...