Hi @michael lustig ,
According to your description, it seems to you have shared your calendar to others, is it right? If so, how did you share it (via exchange delegate or others)?
As I know, in the point of Outlook client, there seems to be no option that could track it. But based on my research, if you actually shared your calendar via delegate and would like to log what account accesses the mailbox and what changes are made to the contents, we could enable auditing in Exchange and use the Search-Mailbox cmdlet to view the logs. For more detailed information, please refer to this article : Logging changes made to items in to a shared Exchange mailboxes.(Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)
Hope that would be helpful to you, and if that's not your case or you still need further assistance, please feel free to post back.
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