By default, a GAL contains mail recipients from a single forest. If you have a cross-forest environment, you can use the GAL Synchronization feature in Microsoft Integration Identity Server (MIIS) 2003 or in the Identity Integration Feature Pack for Microsoft Windows Server Active Directory with Service Pack 2 (SP2) to ensure that the GAL in any given forest contains mail recipients from other forests. This feature creates mail-enabled contacts that represent recipients from other forests, thereby allowing users to view them in the GAL and send mail. For example, users in Forest A appear as contacts in Forest B and vice versa. Users in the target forest can then select the contact object that represents a recipient in another forest to send mail.

To enable GAL Synchronization, you create management agents that import mail-enabled users, contacts, and groups from designated Active Directory services into a centralized metadirectory. In the metadirectory, mail-enabled objects are represented as contacts. Groups are represented as contacts without any associated membership. The management agents then export these contacts to an organizational unit in the specified target forest.

For more information about deploying MIIS 2003, see Microsoft Identity Integration Server 2003 TechCenter. For more information about downloading Identity Integration Feature Pack for Microsoft Windows Server Active Directory with Service Pack 2 (SP2), see Identity Integration Feature Pack for Microsoft Windows Server Active Directory with Service Pack 2 (SP2).

In a cross-forest topology in which both forests have Exchange 2007, and users use Microsoft Office Outlook 2007 to access their e-mail, you can use the Availability service to gather free/busy data about users in both forests. For more information about the Availability service, see Managing the Availability Service.

In a cross-forest coexistence topology, in which one forest does not have any Exchange 2007 Mailbox servers, or users do not use Outlook 2007 to access their e-mail, you must use the Microsoft Exchange Server Inter-Organization Replication tool to share free/busy data across forests. For more information, see Microsoft Exchange Server Inter-Organization Replication.

Note:

It is supported to install the Inter-Organization Replication tool on a computer that has the Exchange 2007 management tools installed without any Exchange 2007 server roles, or on an Exchange 2003 or Exchange 2000 server. If you install the Inter-Organization Replication tool on a computer that has the Exchange 2007 management tools installed, you must also install the Exchange MAPI client libraries. For more information about the Inter-Organization Replication tool, see Microsoft Exchange Server Inter-Organization Replication. For more information about downloading the Exchange MAPI client libraries, see Microsoft Exchange Server MAPI Client and Collaboration Data Objects 1.2.1.

In a cross-forest topology, you may want to move mailboxes from one forest to another. To do this you must use the Move-Mailbox cmdlet. This is the same command that you use to move mailboxes within a single forest.

Note:
You cannot use the Move Mailbox wizard to move mailboxes across Exchange Server 2007 organizations. To move a mailbox from one Exchange Server 2007 organization to another, you must use the Move-Mailbox cmdlet in the Exchange Management Shell.

For more information about moving mailboxes, see Moving Mailboxes.

• For more information about deploying Exchange 2007 in a new cross-forest topology, see How to Deploy Exchange 2007 in a Cross-Forest Topology.
  
  
• For more information about deploying Exchange 2007 in a new resource forest topology, see How to Deploy Exchange 2007 in an Exchange Resource Forest Topology.
  
  
• For more information about transitioning an existing Exchange topology to an Exchange 2007 topology, see Upgrading to Exchange 2007.