Unable to read calendars of all users in my tenant

Question

I am trying to read calendars of all users in my tenant using MS graph API in Microsoft Graph Explorer. I tried using this URI: https://graph.microsoft.com/v1.0/users/{user-id}/calendars but I was unable to get the calendars of other users in my tenant other than mine. I gave all the permissions that the Graph Explorer asked for as shown in the screenshot below but I am getting this error: { "error": { "code": "ErrorItemNotFound", "message": "The specified object was not found in the store.", "innerError": { "date": "2023-05-18T04:38:16", "request-id": "..............................................................................", "client-request-id": "..................................................................." } }

Is it actually possible to read other users' calendars who are in my tenant? If so, how or where am I making a mistake?

I tried using this URI: https://graph.microsoft.com/v1.0/users/{user-id}/calendars but I was unable to get the calendars of other users in my tenant other than mine. I gave all the permissions that the Graph Explorer asked for as shown in the screenshot below but I am getting this error: { "error": { "code": "ErrorItemNotFound", "message": "The specified object was not found in the store.", "innerError": { "date": "2023-05-18T04:38:16", "request-id": "..............................................................................", "client-request-id": "..................................................................." } }

Answer 1

There are two levels of permission that you need when accessing another mailbox. The first is Calendar.Read.Shared that give you application the ability to query the endpoint. Then the user making the query need underlying Folder permissions so they would either need to be a Mailbox Delegate or granted at least reviewer permissions set with either https://learn.microsoft.com/en-us/powershell/module/exchange/set-mailboxfolderpermission?view=exchange-ps or through Outlook by the user.

The error message isn't really helpful in this instance "The specified object was not found in the store." it means your accessing Exchange okay but because of the permissions you can't access the folder.