Hi,
We have started migrating from Exchange 2016 to Exchange online. This migration will take around 2 months to complete, and meanwhile we will be running a Hybrid environment.
After we have migrated the first few users, we have noticed that users with a mailbox in Exchange Online are unable to see the calendar of users with an on prem mailbox. They get the error "Could not be updated".
Exchange online users are able to see the calendar of other exchange online users. The default calendar sharing permission for all users is: My organization > Can view when I'm busy.
Any idea where to look into?
Thanks in advance.
you can find here a little guide to investigate :
https://docs.microsoft.com/en-us/exchange/troubleshoot/calendars/troubleshoot-freebusy-issues-in-exchange-hybrid#does-freebusy-work-on-premises
Particularly here :
https://docs.microsoft.com/en-us/exchange/troubleshoot/calendars/troubleshoot-freebusy-issues-in-exchange-hybrid#cloud-user-cant-see-on-premises-users-freebusy
Did you choose to install an hybrid agent or the classical installation?
In the classical configuration, your should verify that Web services (/EWS) are accessible from Internet.