Your company has a main office and 50 branch offices. Each office is configured as an Active Directory site. Each branch office site contains a domain controller. 
The main office site contains all the global catalog servers in the forest. Each branch office contains a WAN link that connects to the main office. 
You need to plan the deployment of new Mailbox servers to meet the following requirements：
.Ensure that users in the branch offices can access their mailboxes if their local domain controller fails.Deploy the minimum number of Exchange servers
What should you include in the plan？（）

Your network consists of an Active Directory domain that contains the domain controllers shown in thefollowing table.You plan to deploy an Exchange Server 2010 server in each site. 
You need to recommend changes to the domain controllers to support the installation of Exchange Server2010.
What should you do？（）