Here is a description of the problem and the eventual resolution which took a few days and late nights to resolve:
Scenario
With a recent deployment of Exchange Server 2013 CU6 in a
hybrid configuration with Office 365 user that had mailboxes on O365 couldn’t
query for free/busy of on-premises users.
Users with on-premises mailboxes could query the free/busy status of
O365 mailboxes. The free/busy test for
Office 365 in the Exchange Remote Connectivity Analyser (http://exrca.com ) showed the test for free/busy
queries from O365 to on-premises as working successfully.
Environment
·
A multi-domain Active Directory forest with all DCs
running Windows Server 2012R2
· A single Exchange Server 2013 CU6 server with Mailbox/CAS roles installed, running on Windows Server 2012R2
· DirSync and ADFS running on Windows Server 2012R2
· Exchange Hybrid configured by running the hybrid configuration wizard on the Exchange Server 2013 CU6 server
· Clients running Windows 8.1 and Outlook 2013 SP1
· Clients running IE11 and connecting to OWA on the O365 portal
