I started to update client exchange servers to the latest CU (one client uses 2013 standard and another 2016 standard). Both updates deleted dll files from the directories. One server i was able to restore them from a backup to get the exchange services running. The other server however i am not so fortunate. no exchange services will start. They were left in a disabled state after the update failed. restoring a backup i took before the update ran into problems because the machine account lost its trust with the domain controller, removing and readding did not solve the problem - additionally, exchange doesn't show as being installed in add remove programs. I have been waiting over a week for Microsoft support to respond, all i get are notices that it is taking longer than normal to assign a tech. We have already been forced to route mail to an cloud provider just to get email but we still need our history. I am posting this as a warning to anyone who is looking to install the latest CU. Make sure you have a very good disaster recovery plan because this affected 2 out of 2 exchange server i tried it on (a 2013 and 2016). Shame on Microsoft for releasing such a horrible patch, there is no way something like this should ever happen with a failed update.