We recently upgraded client office applications from Office 2013 Standard to O365 Pro Plus. (Outlook 2016).
When creating or sharing any calendars - the user is not sending the invite, and invited user does not see a calendar to open manually.
We are running a hybrid exchange environment - exchange 2010 and O365.
The user/s in question both have not been migrated (on-prem) and live on exchange 2010.
We can share calendars and send invites as expected as O365 Migrated users.
On-Prem or legacy non-migrated users can no longer share calendars since upgrading the local client software. No email or invitation is sent.
We cannot find the shared calendar manually.
Any assistance would be appreciated.