cleanfolderperms.ps1

$user = "NT User:S-1-5-21-579602563-1105609867-1454996784-1641"
$mailbox = "someuser@contoso.com"
$folders = @(Get-MailboxFolderStatistics $mailbox | Where {!($exclusions -icontains $_.FolderPath)} | Select FolderPath)
foreach ($origFolder in $folders) {
  $id = $mailbox + ":" + $origFolder.FolderPath.Replace('/','\')
  # Uncomment this to list all unattached sids
  # get-MailboxFolderPermission -Identity $id | where {$_.user -like "*S-1-5*"}
  # Remove dead permissions
  if ($perm = get-MailboxFolderPermission -Identity $id -user $user -ErrorAction SilentlyContinue) {
    remove-MailboxFolderPermission -Identity $id -user $user -Confirm:$false -ErrorAction STOP
    write-host "Removed $id " + $perm.User 
  }

}