How to generate a report on Exchange Mailbox events?
Perform the following steps to generate a report from Exchange Mailbox events:
When you click on any one of the recent events based reports, a dialog will appear as shown below, for user selection, whose events you would like to see in the generated report

If you would like to view events for a specific user, select the "Specific users" option, and select the list of users by clicking on the "Select users" button

For Top users based report, a dialog will appear as shown below for selecting events and date range for fetching the list of top users who had performed the Exchange mailbox events recently
Once you click on "OK", the report will be generated like all the other Audit Reports.