Public/Configuration/Add-DefaultCalenderPolicy.ps1

function Add-DefaultCalendarPolicy {
    param(
        [Parameter(Mandatory)]
        [string]$TenantId
    )

    try {
        Write-ModuleLog -Message "Adding default calendar policy for tenant $TenantId" -Level Info -Component 'Add-DefaultCalendarPolicy'
        Connect-CustomerExchange -CustomerTenantId $TenantId

        Get-Mailbox | Where-Object Name -NotLike 'Discovery*' | ForEach-Object {
            $mail = $_.UserPrincipalName
            Write-ModuleLog -Message "Creating default policy for $mail" -Level Info -Component 'Add-DefaultCalendarPolicy'
            $calendarName =(Get-EXOMailboxFolderStatistics -Identity $mail -Folderscope Calendar | Where-Object FolderType -eq 'Calendar').Name
            Set-MailboxFolderPermission $mail":\"$calendarName -User Default -AccessRights Reviewer
        }
    }
    catch {
        throw $_
    }
}