Troubleshoot Outlook 2010 Cached Exchange Mode

Office 2010

Topic Last Modified: 2012-03-14

You can solve problems that you may encounter when you set up or use Cached Exchange Mode in Microsoft Outlook 2010.

This article describes Cached Exchange Mode issues that you might face and provides help for resolving them. For more information, see the Outlook IT Pro Discussions ( ) forum.


If, in a Microsoft Exchange Server 2010 environment, you are running Microsoft Office 2010 on clients that are running either Windows Server 2008 R2 or Windows 7, you may want to disable Cached Exchange Mode for Remote Desktop Server. Users who have portable computers must have Cached Exchange Mode enabled. However, when they log on to the Remote Desktop server, their .ost files are copied as part of their profiles. As a result, too much disk space is used. In this case, it is best to keep Cached Exchange Mode for the clients but disable it for the Remote Desktop server.

To do this, on a Group Policy object (GPO) that is specific for Terminal Servers, set the Use Cached Exchange Mode for new and existing Outlook profiles policy setting to Disabled. You can find this policy setting in the Group Policy object editor, under User Configuration\Administrative Templates\Microsoft Office Outlook 2010\Account Settings\Exchange\Cached Exchange Mode. For more information about how to edit a GPO, see Editing a GPO.

This process sets the following registry key value:

HKEY_CURRENT_USER\Software\Policies\Microsoft\office\14.0\outlook\cached mode

Enable = 0

For more information about Group Policy, see Use Group Policy to enforce Office 2010 settings.

For more information planning for Cached Exchange Mode in Remote Desktop Server, see Cached Exchange Mode in a Remote Desktop Session Host environment: planning considerations (

You might receive a "sync issues" error message when you send an email message by using Outlook 2010 with Cached Exchange Mode enabled. It occurs shortly afterward, when an error is logged in the Sync Issues folder.

You can work around this issue by stopping the Modification Resolution logs, which provide a description of the actions that Outlook took during a conflict situation. To stop the Modification Resolution logs, configure a registry key as described in the following table, and set the value to 0:



HKEY_CURRENT_USER\ Software\Microsoft\Office\14.0\Outlook\Options




0 = Never save Modification Resolution logs

1 = Always save Modification Resolution logs

2 = Save Modification Resolution logs when a "critical conflict" occurs

This issue occurs when Outlook 2010 is running in Cached Exchange Mode with a retention policy that is applied to a folder (for example, the Deleted Items folder). This policy requires items to expire and be removed from the folder after a certain time. When you use Outlook to view the folder, items that are older than this expiration date appear to be expired as expected. However, these items are not removed from the server. (You will notice this if you use Outlook Web Access to look at the folder.)

This issue occurs because Outlook calculates the expiration date when Outlook is in Cached Exchange Mode (or offline mode), while Exchange Server specifies the expiration date when Outlook is in online mode. When you work in online mode, the issue is not present.