I ran into an interesting problem during a deployment of OCS at a client that had Exchange 2007 deployed but had no set up Exchange OWA for external access.
Every time I log into MOC, I would notice that the top right hand corner of the client indicates that there’s a problem with a service:
When I click on the error to bring up the details, I would get the following message:
Here's the error:
Communicator could not retrieve calendar or Out of Office information from Exchange Web Services. Communicator will automatically continue to retry. If this problem persists, contact your system administrator.
As it turns out, the OOF information is retrieved through the IIS websites on the CAS server and since the CAS server was never set up for proper external access, it was still using a self-signed certificate that wasn’t trust. During the troubleshooting process, I noticed that if I were to navigate to https://cas/owa, I would get a notification that the certificate wasn’t trusted. From there on, I requested a certificate from the internal CA, bind-ed it to the website and noticed that the error from my MOC client was gone.
Seeing how most organizations deploy OWA in some form or shape, I would have never ran into this problem if OWA at those companies because a public certificate would have been used.