Exchange Server 2010 can be installed in an on-premises, cloud, or coexistence configuration.
SLA requirements determine parts of your Exchange design, primarily around high-availability features such as Database Availability Groups and Client Access Server Arrays.
In multiple-forest environments, the resource-forest topology has Exchange deployed in one forest and accessed by users in other forests. The cross-forest topology has Exchange deployed in all forests and uses Forefront Identity Life Cycle Manager for GAL synchronization.
Ensure that there is at least one Hub Transport server in every site where there is a Mailbox server on a per-forest basis.
ActiveSync allows supported mobile devices to access mailbox data.
You can configure Autodiscover to automatically provision Outlook 2007 and Outlook 2010 clients.
The Load Generator (LoadGen) tool can be used to test a CAS against a simulated client workload.
JetStress allows you to test how well a mailbox server handles simulated load. LoadGen allows you to simulate CAS load. Both tools can be used when determining whether it is feasible to consolidate existing servers.
When performing an upgrade, Internet-facing sites must be upgraded before sites that do not have a direct Internet connection.
When upgrading from previous versions of Exchange, introduce CAS to a site first, then Hub Transport, and then Mailbox servers. Add Edge Transport servers at Internet-facing sites as appropriate.
The Exchange Server Deployment Assistant can analyze a current environment prior to the introduction of Exchange Server 2010.