Exchange 2010 Cross-Forest Mailbox Moves

We are seeing some trends where quite a few customers are migrating mailboxes to a new Exchange organization, in a different Active Directory (AD) forest. This blog post is aimed at helping to explain the fundamentals of what is required to move mailboxes across forests so that you can be prepared with the correct data, make better plans, and successfully perform a migration without encountering painful problems. The blog post doesn't cover how to setup and configure shared address space or Free/busy.

After reading this blog post, you should have better understanding of:

• How to plan your migration by understanding your current forest configuration and your desired configuration.
• Different ways for you to synchronize user data between different AD forests.
• Networking and Administrator permissions required to perform a successful cross-forest mailbox move.

The trends we are seeing currently show that companies are having more trouble understanding the different scenarios than performing the migration. There are several scenarios here, and Microsoft has tools, documentation, and scripts to assist in each one of them.

There are many reasons companies choose to have multiple forests or maybe find themselves with multiple forests, requiring cross-forest moves of users and mailboxes. For instance:

1. Companies that merge, are bought out, or have absorbed another company in some manner.
2. Companies who want to start fresh and leave a lot of legacy issues behind.
3. Companies that have subsidiaries; segment their environment by Department, Geography, or for Security considerations.

The common Active Directory topologies that are supported in Exchange 2010 are as follows:

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

Exchange deployment topologies vary due to organizational size and business complexity. Variations may include Single Forest, Resource Forest, Hybrid Forest, and Cross Forest topology. For purposes of discussion the following forest definitions will be used going forward:

Forest Name	Active Directory user object status	Mailbox Status
Exchange Forest	Enabled User Object	Mailbox Enabled
Account Forest	Enabled User Object	No mailbox enabled objects
Resource Forest	Disabled User Object (linked to a separate enabled user object in an Account Forest)	Mailbox Enabled
Hybrid Forest	Both 1.) AD Enabled Mailbox Enabled 2.) AD Disabled Mailbox Enabled	Both mailbox enabled and disabled objects

Most of the Cross-Org Move Mailbox scenarios are closely related to the Active Directory Forests involved in the migration. There are 3 major scenarios to be considered:

--> To be seen on the Exchange Team Blog! :

http://msexchangeteam.com/archive/2010/08/10/455779.aspx