Mailbox size matters, but concentration, item count and change over time provide the context needed for archive, retention, licensing or clean-up decisions.
1. Measure size concentration
Begin with the largest mailboxes, then compare their combined storage with the tenant total. If a small group accounts for a large share of capacity, a focused review may be more useful than a tenant-wide response.
Record mailbox type alongside size. A large user mailbox, shared mailbox and room mailbox may each require different questions about ownership, purpose and future use.
2. Review the largest mailboxes in context
A large mailbox is a review signal, not a diagnosis. Check whether it belongs to an active user, a role-based account, a former employee or a business function with legitimate long-term history.
- Current mailbox and archive size
- Mailbox type and accountable owner
- Relevant licensing or archive configuration
- Operational or compliance reasons for retaining content
3. Treat high item counts as a separate signal
Two mailboxes with the same size can behave differently when one contains many more items. High item counts can point to automated notifications, long-running workflows or mailboxes used as informal records.
4. Look for fast growth
A point-in-time assessment identifies current pressure. Repeatable reporting adds direction: which mailboxes are growing fastest, whether archives are absorbing growth and whether pressure is concentrated or widespread.
5. Build evidence before selecting an action
Use the findings to define what needs investigation. Archive enablement, retention changes, licensing review and user-led clean-up each have different implications. Evidence helps administrators avoid applying one response to every large mailbox.
Summarise the tenant total, top mailboxes, item-count outliers, archive signals and priority review candidates. MailboxVitals provides metadata-led assessment and recommendations to support that decision process; changes remain under administrator control.