Exchange Server users can connect to Microsoft Outlook 2007 in cached or online mode. Enabling cached mode creates an .OST file within the user's profile. Outlook uses this file to store a copy of the user's Exchange Server data. This allows mobile users to access an offline copy of their mailbox items, even if they're not connected to Exchange Server.
There are a number of different configurations for Outlook in cached mode and associated .OST files. You can set these options manually, but it's better to apply them at the group policy level so they're consistent across your entire Exchange organization.
Note: Before you can control .OST file settings on client machines, you must install the Office 2007 Administrative Template files. These files add Microsoft Office group policy settings to the Group Policy Object Editor.
Once the necessary templates are in place, you can configure .OST file group policy settings. These settings are located at: User Configuration -> Administrative Templates -> Microsoft Office Outlook 2007 -> Tools -> Account Settings -> Exchange. This location contains other group policy settings unrelated to .OST files.
Synchronizing data in shared folders -- This setting prevents .OST files from being filled with useless data. It allows you to set a limit to the amount of time that Exchange Server data is synchronized with an .OST file.
Suppose that you set this folder to impose a 60-day synchronization limit. If a user has a folder that he rarely accesses, the folder's contents will remain synchronized. However, if the user doesn't access the folder for 60 days, synchronization between the Exchange server and .OST file is disabled for that folder. Outlook also deletes the folder's data from the .OST file. If the user accesses the folder again, Outlook will re-establish synchronization.
Cached Exchange low-bandwidth threshold value -- This setting allows you to instruct Windows what low bandwidth is. For example, you might instruct it to download message headers to an .OST file, instead of downloading the entire message if sufficient bandwidth isn't available.
Do not allow an .OST file to be created -- This setting is similar to selecting Outlook's Disable Offline Use option, which is located in the Offline Folder Settings dialog box.
Exchange Unicode Mode - Ignore .OST Format -- Outlook can be configured to determine if it should run ANSI or Unicode mode by examining the format of the user's .OST file. Prior to Office 2003, Microsoft Outlook used the ANSI format for .PST and .OST files. ANSI-based files had a 2 GB size limit and data loss could occur if this limit was exceeded. Outlook 2003 and Outlook 2007 can use Unicode mode instead, which has no size limit.
About the author: Brien M. Posey, MCSE, is a five-time recipient of Microsoft's Most Valuable Professional (MVP) award for his work with Exchange Server, Windows Server, Internet Information Services (IIS), and File Systems and Storage. Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Brien has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal website at www.brienposey.com.
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