20 AUGConfiguring Lync Server 2010 to use more than two Exchange Unified Messaging servers

This gotcha was brought to my attention by Ari Protheroe during a recent deployment where a Lync Server 2010 Front End pool needed to communicate with an Exchange Unified Messaging dial plan that consisted of more than two servers. This is an important one to know during the planning/deployment phase of a scaled/resilient environment to ensure all the UM servers you’ve deployed are actually being utilised by every Front End server.

Setting the Scene

This setting is controlled by a process called ExumRouting which runs on each Lync Front End server in a pool. This process is responsible for routing calls from Lync to Exchange Unified Messaging servers to receive voice mail for Enterprise Voice users and to answer calls to the Subscriber Access number (plus any Auto Attendants you may have setup). If this process isn’t running or isn’t working properly, users won’t receive voice mail.

By default in Lync Server 2010, ExumRouting will only try to use 2 servers in the dial plan it’s associated with. If your dial plan consists of more servers than this, you’ll want to change this setting to use all the servers you have deployed.

Making the Fix

To fix this, we need to modify the ExumRouting.exe.config file. On the Lync Front End server, browse to C:Program FilesMicrosoft Lync Server 2010ServerCore and open ExumRouting.exe.config in Notepad as shown below:


Find the key named ExumNumberOfServersToTry and modify the value from the default of 2 to however many UM servers are in the dial plan for your Lync pool (in my case it was 4). Save and close this file and repeat this process on each Front End server in your pool.

For this change to take affect, you will need to restart the Lync Server Front-End service on each Front End server. No service restarts are required on the UM servers.

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