The Calendar Checking Tool (CalCheck) has been around for a long while. It allows IT to dig into Outlook calendars, hosted on Exchange, and diagnose and fix most problems. It checks things like permissions, free/busy records, and other things that might cause problems with the Outlook calendar.
CalCheck has now been updated to provide support for Windows 10 and Outlook 2016. Still a command-line program after it runs will produce a report that can be used to help diagnose problems or identify trends.
Note that CalCheck does not with IMAP, POP3, or other non-Exchange email accounts. The Outlook calendar must reside on the Exchange Server.
Grab the updated version here: Calendar Checking Tool for Outlook - Version 2.5.1
To learn how to use CalCheck and get the list of available command-line switches see knowledge base article 2678030.