Planning for Exchange Active Directory Design

Because Exchange Server 2010 uses Active Directory for its underlying directory structure, it is necessary to link Exchange with a unique Active Directory forest.

In many cases, an existing Active Directory forest and domain structure is already in place in organizations considering Exchange 2010 deployment. In these cases, Exchange can be installed on top of the existing AD environment, and no additional AD design decisions need to be made. It is important to note that Exchange 2010 can be installed only in a Windows Server 2003 functional level (or greater) Active Directory forest, and Windows 2000 functional level forests are not supported. Windows Server 2008 R2 or the latest AD functional level is recommended.

In some cases, there may not be an existing AD infrastructure in place, and one needs to be deployed to support Exchange. In these scenarios, design decisions need to be made for the AD structure in which Exchange will be installed. In some specific cases, Exchange may be deployed as part of a separate forest by itself. This model is known as the Exchange Resource Forest model. This is often the case in an organization with multiple existing AD forests.

In any case, AD should be designed with simplicity in mind. A single-forest, single-domain model, for example, will solve the needs of many organizations. If Exchange itself is all that is required of AD, this type of deployment is the best practice to consider.

Microsoft has gotten serious recently about support for Exchange Server across multiple forests. This was previously an onerous task to set up, but the ability to synchronize between separate Exchange organizations has been simplified through the use of a product called Forefront Identity Manager (FIM). FIM now comes with a series of preconfigured scripts to replicate between Exchange forests, enabling organizations that, for one reason or another, cannot use a common forest to unite the email structure through object replication.