Outlook Web App (Formerly Outlook Web Access) enables the integration of OWA and Instant Messaging, utilizing Office Communications Server (OCS) R2. This requires manual configuration on the Client Access Server and the OCS Front-end. This is documented in Technet here.
Step 1: Download and Install the Microsoft Office Communications Server 2007 R2 Web Service Provider on the Exchange 2010 CAS Server. The installation actually just dumps some additional files that need to be installed into this directory: C:\Web Service Provider Installer Package
If the installation was successful, this registry key should exist:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchange OWA\. The string under InstantMessaging with the name ImplementationDLLPath and the value "<Your Exchange Install Path>\ClientAccess\owa\bin\Microsoft.Rtc.UCWeb.dll"
Step 2: Gather Certificate Information
get-exchangecertificate | fl
Note the Issuer and Serial Number – they’ll be needed in the next step
Step 3: Edit the OWA Web Config File (Located <install drive>\Program Files\Microsoft\Exchange Server\V14\ClientAccess\Owa). Notice the spaces between each set of two digits.
Step 4: Run this powershell command on the CAS Server:
Get-OwaVirtualDirectory –Server CATINEXC05 (replace with your CAS) | Set-OwaVirtualDirectory -InstantMessagingType OCS
Step 5: Add CAS FQDN (internal and external) to Front-End host authorization Tab
According to the Exchange 2010 Unleashed book – you should also select ‘Throttle as Server’ and ‘Treat as Authenticated’
Step 6: Restart IIS on CAS.
Step 7: Restart Front-End Service on OCS (To allow changes to take effect immediately). I waited an hour and the changes did not take effect, and I was getting SIP/2.0 401 Unauthorized errors on the Front-End Logging Tool Trace. But after restarting the front-end service, I can now see presence within Outlook Web App!