Also, the user can no longer view the Calendar folder, and the user receives a "Could not be updated" error.
If a remote user must be able to see free/busy information for the mailbox, the mailbox owner can work around this issue by changing the default permissions to Free/Busy time or Free/Busy time, subject, location. This changes the free/busy information that is shared for all remote users. For example, the default permissions can be set to Free/Busy time:
Remote users can see the free/busy data in Scheduling Assistant:
Or, remote users can see the free/busy data as an additional calendar:
A remote user can be granted Calendar folder permissions to obtain additional access to the contents of the Calendar folder:
The remote user (Test User 1) can now see the mailbox Calendar folder:
There are some differences with contributor permissions when you set the default calendar permissions or when you explicitly grant a user calendar permissions. When the default calendar permissions are set, the Free/busy setting uses None.
When a user is granted contributor rights, the permission level will automatically change to Custom. This includes Free/Busy time.
This is expected behavior, because users who can create items in a calendar can also see the folder and view free/busy information.