Microsoft 365 Reports in the admin center - Mailbox usage
https://learn.microsoft.com/en-us/microsoft-365/admin/activity-reports/mailbox-usage?view=o365-worldwide
WEBJan 17, 2024 · From the Email activity drop-down list, select Exchange > Mailbox usage. Interpret the Mailbox usage report. You can get a view into your organization's mailbox usage by looking at the Mailbox, Storage and Quota charts. To access shared mailbox information, change the drop-down selection at the top right of the charts to Shared.
DA: 6 PA: 21 MOZ Rank: 83