The UseLegacyFB registry value does not work as expected in Outlook 2010 and Outlook 2013

Original KB number:   982698


If you add the UseLegacyFB registry value to the Windows registry to try to force Microsoft Outlook 2010 or Outlook 2013 to behave like Office Outlook 2007, the value is ignored by Outlook.


The UseLegacyFB registry value is not used by Outlook 2010 or Outlook 2013. By default, if your mailbox is located on a Microsoft Exchange 2007 or Exchange 2010 server, Outlook 2007, Outlook 2010, and Outlook 2013 use the Exchange Availability Service to locate free/busy information. This is a change from Outlook 2003 and earlier versions of Outlook that use public folder free/busy information.


Public folder free/busy was removed from Outlook 2013. For more information about changes in Outlook 2013, see Changes in Office 2013.

In Office Outlook 2007, you can use the following registry data to force Outlook 2007 to use public folder free/busy information instead of the Availability Service.

Key: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Options\Calendar
Name: UseLegacyFB

Value: 1

In some scenarios where you are troubleshooting Availability Service problems, you might want to force Outlook 2007 to use public folder free/busy information by adding this registry data to the client. In these same situations, you cannot force Outlook 2010 or Outlook 2013 to use public folder free/busy information because the UseLegacyFB registry value is ignored.


If you are troubleshooting Availability Service issues in Outlook 2010 or Outlook 2013, you can enable Availability Service logging. To do this, follow these steps:

  1. Start Outlook.

  2. On the File tab, select Options.

  3. In the Outlook Options dialog box, select Advanced.

  4. In the Other section, select the Enable troubleshooting logging (requires restarting Outlook) check box, and then select OK.

    Screenshot of the Advanced tab on Outlook Options.

  5. Restart Outlook

When Outlook uses the Availability Service to retrieve free/busy information, log files are generated in the following folders:

Outlook 2010


The file name of the log files uses the following format:


For example, a log file that is generated on March 30, 2010 at 2:14:20.0029 P.M. will be named:


Open this log file in a text editor such as Notepad to examine the logging information.

Outlook 2013

%temp%\Outlook Logging

The file name of the log files uses the following format:



To help protect customer data, the advanced trace log files are binary files that cannot be read without a conversion process. You can upload the log files to a secure location provided by Microsoft Customer Support Services. A support engineer from Microsoft can download and convert the log file for analysis. For more information about advanced trace log files, see How to enable global and advanced logging for Microsoft Outlook.