I have a user who belongs to two different Exchange Organizations.  We configured Outlook 2010 to connect to both Exchange servers, but now I need his calendar to synchronize between the two as well.  His Free/Busy info for one company isn't available to the other, so scheduling meetings still requires going back and forth, which I'd like to eliminate.

Has anyone configured this before?  If so, did you need to use 3rd party software?

The Free/Busy informatin is stored in mailbox. We cannot get the solution from Outlook client site.

If you want to sync the Cross-Forest Free/Busy, this article may help you: http://blog.exchange-addict.com/2012/11/cross-forest-freebusy-simple-version_13.html

Or you may use 3rd party software such as Dell's solution: http://www.quest.com/collaboration-services/

Note: This response contains a reference to a third party World Wide Web site. Microsoft is providing this information as a convenience to you. Microsoft does not control these sites and has not tested any software or information found on these sites; therefore, Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. There are inherent dangers in the use of any software found on the Internet, and Microsoft cautions you to make sure that you completely understand the risk before retrieving any software from the Internet.

Tony Chen
TechNet Community Support

Unfortunately, this does not resolve the issue, as it exposes the entire domain.  I have a single user that I need to do this for.  The best/easiest method for me would be some form of rule or sync on his computer that is running Outlook, so that anytime a calendar item is added, removed, or changed, the calendar on the secondary exchange server is updated as well and vice-versa.  Having complete access to domain-wide free/busy is not needed nor wanted.