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.
In this scenario, the information that is required to discover Exchange UM dial plans and route calls to the voice mail cannot be read.
To resolve this issue, install the following cumulative update:
2616433 Description of the cumulative update for Lync Server 2010: September, 2011
To work around this issue, set up a two-way trust between the Exchange Server environment and the Lync Server 2010 environment.
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
975894 Event ID 44031 for trusted domains is logged frequently in Office Communications Server 2007 R2