PS - Exchange Hybrid Free Busy Calendar Issues

Recently when working on a project, following the completion of the Exchange Hybrid Configuration Wizard (HCW). After we had migrated some test mailboxes to Exchange Online, there were problems with Cloud users accessing On-Prem free busy calendar information when scheduling meetings.

The following Microsoft troubleshooting guide can be followed - but this may not resolve your issue.

The issue in this instance was that the client had a TMG in front of the CAS servers with FBA authentication enabled. We had previously had to split the from to use a separate TMG rule with no authentication remembering to limit the source IP's to the office 365 addresses.

First of all Connect to Exchange Online using remote PowerShell.

Execute Get-OrganizationRelationship -Identity * | FL and check the TargetSharingEpr value. If this is blank (default if you have used the HCW) then you will need to populate this value with the host name of the unauthenticated URL in our case

Set-OrganizationRelationship "O365 to On-premises - xxxxxxxxx" -TargetSharingEpr

Once this has been completed, allow time for replication and try this again and hopefully this will resolve your error.

Other articles that may help are