The Mailbox and Public folder size data source is used to produce reports on the size of mailboxes, mailbox folders and public folders. Information displayed in reports is based on a 'snapshot' taken within the last 24 hours. It is dynamically collected through PowerShell. Data is stored into the database and cannot be re-imported for past periods.
For more information about the import process, see Import Storage Size Data .
For more information about the required permissions, see Required permissions and User-based authentication to Office 365.