Exchange 2010 supports the following common Active Directory topologies:

• Single forest, single Active Directory site
• Single forest, multiple Active Directory sites
• Multiple forest, multiple Active Directory sites

Exchange deployment topologies will differ due to organizational size and business complexity. Variations may include Single Forest, Resource Forest, Hybrid Forest, and Cross Forest topology.

Cross forest Migration from Exchange 2010 to Exchange 2010 is as follows:

1. Configure Domain Name System (DNS) for name resolution across forests in organization.
2. Check Windows Power Shell and Windows Remote Management installed in the servers.
3. Create Two-Way trust between forests.
4. Add the respective administrative account in to other forest build-in administrative group or Use RBAC to create custom Role group for cross forest permission group add the respective administrative account in to group.
5. Install the Microsoft Identity Lifecycle Manager (ILM) 2007 Feature Pack 1 (FP1) Service Pack1 or FIM synchronize service in target forest and configure the GAL Synchronization between forests.
6. Install the ADMT3.1 in target forest for account migration.
7. Enable the MRS Proxy in CAS servers on both forests.
8. Export source and target certificates for CAS EWS service (IIS).
9. Export source and target CA root certificate.
10. Import source certificate + source CA root certificate on the target CAS.
11. Import target certificate + target CA root certificate on the source CAS.
12. Create a remote domain (respective FQDN of target forest name) in both forests.
13. Create a Send connector between both forests.
14. Create a Receive connector between both forests.
15. Modify the authentication method that is used for this receive connector.
16. Check mail flow between forests.
17. Prepare Mailboxes for Cross-Forest Moves Using the Prepare-MoveRequest.ps1 script in the Shell. It would create mail contacts in Exchange Organization.
18. Move the accounts from the source forest to target forest using ADMT.
19. Move mailboxes from source Forest to Target forest using remote move request or shell cmdlets.
20. Move the Public folder using outlook 2010 or export it as a PST and import to target PF.
21. Add the source domain name in to accepted domain list in target forest.
22. Educate the user to access the OWA, Active sync and Auto discover of target forest namespaces.