These reports primarily tell the story of how users are consuming mailbox storage.
The Mailbox panel really tells us the same story that we should already know from the Email Activity report, albeit just a bit more explicitly. It shows the number of mailboxes, and how many of those were active on a given day. One assumes that the number of mailboxes corresponds to users plus other mailboxes, such as group, shared, and resource mailboxes—and that a mailbox is active whenever users read or send email with it.
The Storage and Quota panels are marginally more informative.
Since Storage only provides the total for all users, this top-line number is only truly useful in identifying trends over time or perhaps for calculating the cost ...
