We are trying to get group calendars working for Teams we are creating but having issues. When we create a new team in Teams, go to files, select ‘Open in SharePoint’, create a calendar webpart the link to open the group calendar in Outlook redirects to outlook.office365.com/owa which then displays an error ‘We couldn't find a mailbox for this recipient. Either they don't have a mailbox or don't have a license assigned’. We are using on-premise Exchange 2016, is this expected behavior and if so is there any way we can get the calendaring in Teams/SharePoint working with our Exchange system without migrating that to Office 365? (We have enabled O365 group writeback to our local Active Directory and this appears to be working successfully).
Since you are not using Exchange Online and you have Exchange OnPremises, you don't have full functionality you could expect and that's the case you are just facing here. AFAIK, there is not a workaround for this issue