You can't leave voice mails after an Exchange UM Routing application is recovered from an outage in Lync Server 2013

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Lync Server 2013 More...Less

Symptoms

Consider the following scenario:

The Microsoft Exchange Unified Messaging (UM) Routing application on Survivable Branch Appliance (SBA) servers isn't responding and is being disconnected. Additionally, the following events are logged on the SBA servers because of the heavy load:
The Exchange UM servers are removed from the SBA's Authorized Host list.
After a while, the Exchange UM Routing application is automatically enabled and registered.

In this scenario, users who are hosted on the SBA servers can't leave voice mail messages.

Cause

This issue occurs because the Exchange UM servers aren't automatically restored to the SBA's Trusted Server List after an Exchange UM Routing application is recovered from an outage.