After we apply KB5000871 to exchange server 2016 to address 0-day vulnerability of on-premise exchange server 2016, outlook does not display free/busy info any more. Instead, it says no free/busy information could be retrieved. Your server location could not be determined. Contact your administrator. Outlook also displays "We can't show Mailtips right now" message. It sometimes has error 0x00040820 or Errors in background synchronization. In order to apply the new patch on exchange 2016 running windows server 2016, we also had to apply cumulative exchange update 19 (it was on cumulative update 11) and install dot net framework 4.8 in the process. Another thing to note is that we have hybrid Azure online in our domain environment to get access to MS teams. Does anyone have this problem? Did the latest patch break outlook 2013? We just notice that the shared calendars are not working any more. It displays no connection at the top. I would say more things are broken. Thanks, George.