It has been a long time since I last performed the Exchange installation and CU updates. So just to reconfirm something that I wasn't sure about as I can't find back my memory about this. As what I remembered, the prepare schema and AD should only run once in one of the Exchange servers. For example, if I have 3 Exchange servers 2016 with CU16, I have ran the prepare schema and AD commands in one of the Exchange server located in different AD site using CU19 installer and done the upgrade. So when I need to upgrade the rest of the servers I do not need to run the prepare schema and AD again right? How about the prepare domains? If I already executed preparealldomains once do I need to run it again when updating the second server?