More and more mobile clients and apps gain access to our calendar to make our life easier and more comfortable. Also the way we work changed and multiple assistants maintain a single mailbox. In general everything works across multiple platforms and clients. But what when suddenly a few people turn up at your office as all of them have the appointment....except you?In this session you will learn how you can use existing built-in tools to examine the history of calendar items (e.g.: who and what was changed by which client) either on-premises or in Exchange online. There is not always the need for a Microsoft support case. Besides the built-in tools there are also others, build by the community.