http://gallery.technet.microsoft.com/office/Exchange-Online-Dashboard-5454a4a4
1.View Mailbox Info(ItemCount, last Login time, objects, mailbox quota)
2.Check Active Report and Inactive Mailbox Report
3.Export Specific Active and Inactive Report to .csv file
4.Export Specific Mailbox Login Report to .html file
You can use this tool to analyze health status of your organization.
Required install Windows Azure Active Directory Module for Windows PowerShell first
Reference: http://technet.microsoft.com/en-us/library/jj151815.aspx