Get-OutlookItems.ps1

Add-Type -assembly "Microsoft.Office.Interop.Outlook"
$Outlook = New-Object -comobject Outlook.Application
$namespace = $Outlook.GetNameSpace("MAPI")

$i = 0
$j = 0
$topfolder = ""
$inbox = ""
$namespace.Folders | ForEach-Object {
    $i++
    if($_.Name -like 'mailbox@example.com'){
        $topfolder = $namespace.Folders.Item($i)
        #$namespace.Folders.Item($i)
        
        $topfolder.Folders | ForEach-Object {
            $j++
            if($_.Name -like 'Inbox'){
                $inbox = $topfolder.Folders.Item($j)
            }
        }
    }
}
$topfolder.Name
$inbox.Items.Count