Topic Last Modified: 2011-01-26

The Lync Server 2010 ExUM Routing application supports integration with Exchange Unified Messaging (UM) in an on-premises environment, where Lync Server 2010 and Exchange UM are both installed locally within your enterprise, or in with Exchange UM hosted by a service provider, as shown in the following diagram.

The following modes are supported:

• On-premises Mode   Lync Server and Exchange UM are both deployed on local servers within your enterprise.
  
  
• Cross-premises Mode   Lync Server is deployed on local servers within your enterprise and Exchange UM is hosted in an online service provider’s facility, such as a Microsoft Exchange Online data center.
  
  
• Mixed Mode   Your Lync Server deployment has some user mailboxes homed on local servers running Microsoft Exchange Server within your enterprise and some mailboxes homed in a hosted Exchange service data center.
  
  

  Note:
  Mixed mode can be used as a transitional solution during evaluation and stepwise migration of users to hosted Exchange UM, or a permanent solution if you opt to keep some users’ Exchange UM services on-premises after migrating others.

To integrate Lync Server with hosted Exchange UM, you must configure a shared SIP address space (also called a split domain). In this configuration, both Lync Server and the third-party hosted Exchange UM service provider can access the same SIP domain address space. For details, see Hosted Exchange UM Integration Architecture in the Planning documentation.