Both Outlook and our AboutTime for Exchange Server product use free/busy time published by Microsoft Exchange to find available times in user’s calendars.  It’s great to be able to automatically find available time, but is the free/busy time published by Exchange always accurate?  If you are using Outlook 2007 or earlier with MS Exchange 2003 or earlier, the answer is “not all the time.”

Free/busy times in Exchange 2003 and earlier versions are created by having Outlook publish free/busy times to a special public folder.  By default, this information is published every fifteen minutes for the next two months.  In Outlook 2003, you can change these defaults by going into the Tools menu, selecting Options, clicking on the Calendar Options button, and then selecting Free/Busy Options.  You should see a dialog that looks like this:

You can increase the frequency that information is published and the number of months of free/busy information you want to publish.  Increasing either the frequency or the number of months, puts more load on the network and your Exchange servers, but increases the accuracy and availability of free/busy time.

There are other factors that can impact both the availability and the accuracy of Exchange free/busy time:

1. The special public folder is replicated to other Exchange servers at an interval defined by the Exchange system administrator.
2. The free/busy folder can get corrupted.
3. Outlook may be prevented from sending the free/busy messages (e.g., your VPN connection is not available).

In Exchange 2007, web services are used to get the free/busy data in real time.  Public folders are not used, so that issues with inaccurate free/busy data disappear.  For more information on Exchange free/busy time, see:

http://www.msexchange.org/tutorials/FreeBusy-Folders-Exchange-Server-2003-Depth.html

David Greer