We have Lync Server 2013 running in our forest, however we use an Exchange 2013 server that is hosted in another forest for email access. For quite a while we had a problem with the Lync clients being able to connect to Exchange 2013 to be able to access Conversation history, calendars, etc... we figured that it was because of the migration the other forest did from exchange 2010 to 2013 (the exchange integration was working before in exch2010)
We figured out one day that in the credential manager in the Windows Control Panel was missing an entry for Lync EWS authentication which looks something like (after comparing settings to another user who still had integration working):
Internet or network address:Microsoft_OC1:email@example.com:specific:EWS:1
After manually adding this credential for lync clients that had issues, Lync was able to access the Exchange server in the other forest and pull our Conversation History, meetings, etc.
Is there a way that we can force the Lync clients to reprompt and store this credential and keep it in the credential manager? I have about 60 users who use Lync. Please let me know if you need any other information that I may have left out.