To configure free/busy sharing between two federated Exchange 2010 organizations, complete the steps in Configure Federated Delegation for both organizations.

To configure free/busy sharing between Exchange 2007 and Exchange 2010 organizations, follow the steps listed below for each Exchange organization.

1. Add Exchange 2010 SP1 server   An Exchange 2010 SP1 server with the Client Access server (CAS) role must be installed in the Exchange 2007 organization. If you have other existing Exchange 2010 servers, they should also be updated to Exchange 2010 SP1. Learn more about installing Exchange 2010 in an Exchange 2007 organization at Exchange 2007 - Planning Roadmap for Upgrade and Coexistence.
   
   
2. Federated delegation   Configure federated delegation between the Exchange 2007 and Exchange 2010 organizations by completing the steps in Configure Federated Delegation for both organizations.
   
   
3. Active Directory synchronization   Active Directory synchronization must be configured for all users that need to share free/busy information between the organizations. You can either configure the Active Directory synchronization manually or use an automated Active Directory synchronization service. Learn about Active Directory synchronization at Forefront Identity Management.
   
   
4. Availability address space   Create a new availability address space for the remote Exchange 2010 organization that directs availability requests from Exchange 2007 mailbox users to the Exchange 2010 Client Access server in the Exchange 2007 organization. This setting enables user availability requests from Exchange 2007 users for users in the remote Exchange 2010 organization to be proxied through the Exchange 2010 CAS server in the Exchange 2007 organization. The Exchange 2010 Client Access server uses the federation trust and organization relationship to send the availability requests to the remote Exchange 2010 organization forest availability endpoint.
   
   Run the following command in the Exchange Management Shell on the Exchange 2010 Client Access server in the Exchange 2007 organization to configure the availability address space:
   
   

   	Copy Code
   Add-AvailabilityAddressSpace -AccessMethod InternalProxy -ProxyUrl https://<Exchange 2010 CAS server name>/ews/exchange.asmx -ForestName <SMTP domain of the remote Exchange organization> -UseServiceAccount $True

To configure free/busy sharing between Exchange 2003 and Exchange 2010 organizations, follow the steps listed below for each Exchange organization.

1. Add Exchange 2010 SP1 server   An Exchange 2010 SP1 server with the Client Access and Mailbox server roles must be installed in the Exchange 2003 organization. If you have other existing Exchange 2010 servers, they should also be updated to Exchange 2010 SP1. Learn more about installing Exchange 2010 in an Exchange 2003 organization at Exchange 2003 - Planning Roadmap for Upgrade and Coexistence.
   
   
2. Configure federated delegation   Configure federated delegation between the Exchange 2003 and Exchange 2010 organizations by completing the steps in Configure Federated Delegation for both organizations.
   
   
3. Configure Active Directory synchronization   Active Directory synchronization must be configured for all users that need to share free/busy information between the organizations. You can either configure the Active Directory synchronization manually or use an automated Active Directory synchronization service. Learn about Active Directory synchronization at Forefront Identity Management.
   
   

   Important:

   The OU=EXTERNAL (FYDIBOHF25SPDLT) public folder is only created on the Exchange 2010 CAS/Mailbox server if the option to create the public folders is selected during the Exchange 2010 setup. Additionally, this option is only presented during the setup process if the Exchange 2010 CAS/Mailbox server is the first Mailbox server installed in the organization. If the OU=EXTERNAL (FYDIBOHF25SPDLT) database wasn’t created during setup, you will need to manually create this folder. Learn more at: How to troubleshoot Free/Busy issues when you use Exchange Federation in the Microsoft Office 365 for enterprises environment

4. Follow the steps below to configure public folders for free/busy sharing in your Exchange 2003 organization.
   
   
   1. In Exchange System Manager, navigate to Administrative Groups > First Administrative Group > Servers.
      
      
   2. Select your Exchange 2003 server and navigate to First Storage Group > Public Folder Store > Public Folders > Schedule+ FREE BUSY.
      
      
   3. In the action pane, select the OU=EXTERNAL (FYDIBOHF25SPDLT) folder for the First Administrative Group.
      
      
   4. Right-click the OU=EXTERNAL (FYDIBOHF25SPDLT) folder, and then click Properties.
      
      
   5. In OU=EXTERNAL (FYDIBOHF25SPDLT) Properties, select the Replication tab.
      
      
   6. To replicate the OU=EXTERNAL (FYDIBOHF25SPDLT) folder to the Exchange 2010 CAS/Mailbox server, click Add.
      
      
   7. In Select a Public Folder Store, select the Public Folder Database for the Exchange 2010 CAS/Mailbox server and then click OK.
      
      

      Note:
      By default, Exchange uses the replication schedule set on the public folder database.

   8. Click OK to close OU=EXTERNAL (FYDIBOHF25SPDLT) Properties and save your changes.
      
      
   9. Complete the same steps above for the OU=Exchange Administrative Group (FYDIBOHF23SPDLT) folder.
      
      

      Warning:
      Depending on the size of your public folders, this replication could take several hours to complete.

   10. After the OU=EXTERNAL (FYDIBOHF25SPDLT) and OU=Exchange Administrative Group (FYDIBOHF23SPDLT) public folders have replicated to the Exchange 2010 CAS/Mailbox server, you must remove the replicas for these public folders on the Exchange 2003 server.
       
       
5. Modify the LegacyExchangeDN parameter    Modify the LegacyExchangeDN parameter on all mail-enabled objects in the Exchange 2003 organization that reference the remote Exchange 2010 organization. Change the existing organizational unit (OU) value for the mail-enabled object to External (FYDIBOHF25SPDLT). For example, LegacyExchangeDN=/o=First Organization/ou=External (FYDIBOHF25SPDLT)/cn=Recipients/cn=User Name
   
   

The following limitations apply when sharing free/busy information between federated Exchange organizations:

• Outlook Web Access 2003   When a user in an Exchange 2003 organization uses Outlook Web Access to access free/busy for users in a remote Exchange 2010 organization, the request will fail. Outlook Web Access connections from Exchange 2003 can’t make WebDAV (Web-based Distributed Authoring and Versioning) connections to a free/busy system folder to retrieve the free/busy information for remote users. Because Exchange 2010 does not support WebDAV connections, the Exchange 2003 server can't connect to External (FYDIBOHF25SPDLT) on the Exchange 2010 CAS/Mailbox server for Outlook Web Access requests. Outlook clients don’t experience this limitation because they use MAPI instead of WebDAV when connecting to External (FYDIBOHF25SPDLT).
  
  
• Wide Area Network (WAN) latency   In Exchange 2003 organizations, the replicas for all free/busy folders must reside on Exchange 2010 SP1 Mailbox servers. In environments where Exchange 2003 public folder databases are located in multiple physical sites, there may be excessive latency and performance issues if internal free/busy queries have to traverse WAN links to access Exchange 2010 public folder databases not located in the same physical site.
  
  
• Free/busy information period   Free/busy information requests to an Exchange 2007 organization from an Exchange 2010 organization may fail due to a mismatch in the requested free/busy information period. By default, Exchange 2007 accepts availability requests for 42 days of free/busy information and Exchange 2010 may request 62 days of free/busy information. If the request exceeds the default 42 limit imposed by Exchange 2007, the request will fail.
  
  Follow the steps below to configure your Exchange 2007 CAS servers to accept longer period free/busy information requests:
  
  
  1. On all your Exchange 2007 CAS servers, open the following file with a text editor such as Notepad.
     
     <Exchange Installation Path>\V14\ClientAccess\ExchWeb\EWS\web.config
     
     

     Caution:
     Before you make any changes to the web.config file, make a copy of the file and store it in a safe location.

  2. Locate the appSettings section in the web.config file.
     
     
  3. Add a new key “<add key="maximumQueryIntervalDays" value="62" />” and save the web.config file.
     
     

     Note:
     The maximumQueryIntervalDays value isn’t present by default. When this value isn’t present, Exchange 2007 uses the default interval of 42 days.

  4. Stop and restart the Microsoft Internet Information Services (IIS) on all the Exchange 2007 CAS servers.
     
     
• Exchange organizations that have both on-premises and cloud users   If you configure federated delegation with another Exchange organization that is configured in a hybrid deployment with a cloud service such as Microsoft Office 365, free/busy availability lookups for cloud-based or remote users that have been moved to the cloud will fail. Because the organization relationship for your Exchange organization is with the remote on-premises Exchange organization, not the cloud-based Exchange organization, the free/busy request can’t query the cloud-based users. Exchange 2010 doesn’t support functionality to proxy these availability requests through the on-premises organization to the cloud service.