Azure Hybrid & Cloud Migration Blog

Problem:
There is a known issue where sometime with having missing required DNS record entries Lync 2013 client will not be able reflect the user’s mailbox calendar free-busy information. E.g. if you are currently set for a meeting or appointment in your Outlook, and Lync status showing that you are available then there is problem with your Lync Server to communicate with Exchange Server.

Cause:
The possible problem for Lync Server to not able to grab the user mailbox caldera free-busy information is because the AUTODISCOVER.DOMAIN.COM DNS A-Host Record for the SIP primary domain is missing.

Solution:
Make sure that you have autodiscover.domain.com A-Host record entries available in your DNS Server for the entire SIP domain your Lync Server is configured for.

Hope this makes your Lync and Exchange integration more enjoyable.