How to generate Shared Mailbox Access?
Shared Mailbox Access shows the list of all users who have permissions to the shared mailboxes. This report shows information such as Mailbox Name, Mailbox E-mail Address, Identity, User Name, User E-mail Address and Access Rights.
Perform the following steps to generate Shared Mailbox Access:
Select Office 365 Manager from the available vertical tabs. Then from left pane of the application, select Security Reports and then click on Shared Mailbox Access.
On selecting "Shared Mailbox Access" Report, a window is displayed as shown below:
 

     
Once the data collection process is complete, the report data will be displayed in a report window as shown below: