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How to determine the mode that Outlook 2007 or Outlook 2003 is using for offline folder files
Article ID: 831059 - View products that this article applies to.
This article describes how to determine the Microsoft Exchange mailbox mode that is being used for your Offline Folder file (.ost).
The .ost file is the file on your hard disk that contains offline folders. You can create the .ost file automatically when you set up Microsoft Outlook or when you first make a folder available offline. This feature requires you to be using a Microsoft Exchange Server e-mail account.
Starting in Microsoft Office Outlook 2003, a new .ost file format is introduced that offers more storage capacity for both items and folders, and it supports multilingual Unicode data. (Unicode is a character encoding standard that was developed by the Unicode Consortium. By using more than one byte to represent each character, Unicode permits most of the written languages in the world to be represented by using a single character set). An .ost file that is created in Unicode format is not compatible with earlier versions of Outlook, and you cannot open these files in an earlier version of Outlook.
Outlook automatically determines the format that is used to create the .ost file based on the version of the Microsoft Exchange Server that you are using, the administrator settings, and the formats of the data files that are configured for the profile. If your settings do not allow the .ost file to be created in the new format, Outlook creates the .ost file in the format that is compatible with earlier versions of Outlook.
Outlook can use either a Unicode or non-Unicode mode .ost file while running in Cached Exchange Mode.
To determine the mode that you are using, follow these steps.