At my MSP, we like being aware of obscene growth of mailboxes and weird mailbox settings so we can warn our users or help them find a better workflow, This is why we document their mailbox size, and the settings of the mailbox to our documentation system. Our account managers and vCIOs can easily log into the documentation system at a QBR and explain to our clients where they could make some improvements.

To do this, we use the Graph API reporting option. These reports are available for all exchange users and tell us exactly what the current size of the mailbox is, how many deleted items there are and how many items are in use in total.