Consider the following scenario:
- You deploy an on-premises Microsoft Lync Server 2010 environment.
- The environment is integrated with an on-premises Exchange Server environment that has the Unified Messaging (UM) server role installed.
- A one-way trust is set up between the Lync Server 2010 forest and the Exchange Server forest. For example, the Lync Server 2010 forest does not trust the Exchange Server forest, whereas the Exchange Server forest trusts the Lync Server 2010 forest.