I followed the following link to integrate Exchange 2010 OWA with Lync 2013. We have two CAS, so I performed the task on both servers and issued 'iisreset /noforce' on both.

http://www.expta.com/2010/09/how-to-integrate-lync-server-2010-with.html

When I go into OWA, it gives me this message:

Instant Messaging isn't available right now. The contact list will appear when the service becomes available.

Using the Lync debbuging tools, I see these errors:

TL_ERROR(TF_CONNECTION) [0]1374.1494::10/01/2013-16:08:50.877.00000162 (SIPStack,SIPAdminLog::WriteConnectionEvent:1222.idx(374))[1473893138] $$begin_record
Severity: error
Text: The peer is not a configured server on this network interface
Peer-IP: 192.168.0.62:62688
Transport: TLS
Result-Code: 0xc3e93d6a SIPPROXY_E_CONNECTION_UNKNOWN_SERVER
Data: fqdn="domain.com"
$$end_record

The IP address corresponds to one of the two CAS. I have both the internal & external FQDN (which are CNames for the HLB farm IP address) listed as a trusted application server. Do I need to create a trusted application server for each CAS server hostname and not just the load balanced URLs? Can all of these Trusted Application Pool FQDN's use the same port since they are for the same service? Anything else I need to consider?

What I've always done is my trusted application server is the common name on the certificate, which is most likely the same on both boxes.  So if the CN is webmail.domain.com, that becomes my trusted application server and all commands/setup revolves around this name than.

Hope that helps.

Thanks,

Richard

Richard put me on the right track. I found this article which described our situation, where the CN was domain.com. I followed it and now it's working fine.

http://blogs.technet.com/b/dodeitte/archive/2011/12/22/what-fqdn-to-use-when-setting-up-owa-lync-integration.aspx