Give access to calendar based on the user is member of the group.
admin If you need to give auser access to users calendar, based on if there are member of an group, this is the way. Start Exchange Management Shell
calendar
Give all users access to all mailbox calendar
foreach ($Mailbox in (Get-Mailbox -ResultSize Unlimited)) { Add-MailboxFolderPermission -identity “$($Mailbox.Name):\calendar” -AccessRights Author -User default }