We use a local exchange 2016 mail server with outlook 2016 local clients. I have a problem that one of the users, who has outlook installed on his android phone to see his mail, has a problem with the calendar function. When he receives a calendar invitation, it says that the indicated date is busy in his calendar, however, when he checks his calendar, there is no entry for that date (there was no deleted entry for that date). Only on your computer (windows 10 operating system) do you accept or delete calendar entries. Updating outlook did not solve the error.
I have read about the CalCheck program to check for errors like this. I have downloaded the program but I cannot use it because it reports this as an error: "MAPILogonEx failed with error 0x80004005. Check access to the mailbox."