Office 365 User Cannot See On-Premises Free/Busy in Exchange 2010 Hybrid

I encountered an issue recently where, in an Exchange 2010 / Office 365 Hybrid environment, Office 365 users were unable to see calendar and Free/Busy information from On-Premises mailboxes.

I ran through a variety of diagnostic steps, including the “Hybrid Environment Free/busy Troubleshooter” https://support.microsoft.com/common/survey.aspx?scid=sw%3ben%3b3526&showpage=1 and the Free/Busy test on the Office 365 of the Remote Connectivity Analyzer https://testconnectivity.microsoft.com/tests/o365

Neither tool registered an error or indicated a configuration problem.

Eventually, I took a look at the state of the Federation Trust using Test-FederationTrust from the On-Premises Exchange server which returned:

A couple minutes later, calendar and Free/busy sharing were working as expected.

<hat tip> https://blogs.4ward.it/exchange-hybrid-freebusy-not-working-between-onprem-and-office365/

Shane Skriletz , PEI