Office 365 offers a variety of reports about a tenant that you can easily accessed through the admin center. If you need to check on your mailboxes, sites, DLP policies, or general tenant health, the reporting section is a good place to start.
To access reports, simply click on REPORTS in the sidebar of the admin center. The video above will show you where to begin exploring reports, and highlight an example report on mailbox usage. Some reports, like the example in the video, contain data that can be exported to a CSV file. Keep in mind that your available reports will depend on the type of Office 365 plan you have as well as the admin role of the user accessing the report.
For more information, check out this Office 365 support article on reports about service usage or BetterCloud’s info on reporting.