The other day I had to validate and solve a problem with calendar synchronizations between Office 365 and Exchange 2010 (and vice verse). I was aware that On-Premises users could see the status of all users calendars, but Office 365 users only could see the Office 365 users status. (Office 365 users were not able to view F/B information of On- Premises user mailboxes).
This scenario is valid for Exchange 2010/2013 and Office 365 hybrid architectures with or without ADFS. The errors that I had were this:
Trying to share a Calender between On-Prem and an Office 365 User:
"One or more users cannot be added to the folder access list"The outlook/webmail calendar had errors:
"No Information. No free/busy information could be retrieved"
"The recipient's server could not be contacted. Contact your administrator"
Let's see the necessary steps for the resolution.