Mailbox Usage Report

Per-mailbox storage consumption, item counts, and quota status. Identifies mailboxes approaching quotas or with unusual growth across all managed tenants.

Overview

The Mailbox Usage Report provides detailed storage and usage information for every mailbox in your Exchange Online environment. Use this report to monitor quota consumption, identify oversized mailboxes, and plan storage management strategies.

Report Columns

Column	Description
User	Display name and email address
Mailbox Type	User, Shared, Room, or Equipment
Storage Used	Current mailbox storage consumption
Quota	Assigned mailbox storage quota
Quota Used %	Percentage of quota consumed
Item Count	Total number of items in the mailbox
Deleted Items Size	Storage consumed by deleted items
Archive Enabled	Whether Online Archive is configured
Archive Size	Storage consumed in the archive mailbox
Last Activity	Date of the most recent mailbox activity

Quota Status Overview

Mailboxes are categorized by their quota consumption:

Healthy (0-70%) — Within normal usage
Warning (70-85%) — Approaching quota limits
Critical (85-95%) — Near capacity, action recommended
Full (95-100%) — At or exceeding quota, user may be blocked from sending

Warning: Mailboxes at 100% quota will prevent users from sending new messages. Monitor critical mailboxes and take action before they reach full capacity.

Filters

Date Range — Last 7 days, 30 days, 90 days, or custom
Mailbox Type — User, Shared, Room, Equipment
Quota Status — All, Healthy, Warning, Critical, Full
Domain — Filter by email domain
Tenant — Filter by managed tenant

Recommended Actions

Enable Online Archive for users with large mailboxes
Apply retention policies to manage mailbox growth
Increase quotas for legitimate power users
Investigate inactive mailboxes consuming significant storage

Graph API Data Sources

GET /reports/getMailboxUsageDetail
GET /reports/getMailboxUsageStorage
GET /reports/getMailboxUsageMailboxCounts
GET /reports/getMailboxUsageQuotaStatusMailboxCounts

API Reference

GET /api/reports/exchange/mailbox-usage — Get mailbox usage report
GET /api/reports/exchange/mailbox-usage/summary — Get aggregate statistics
POST /api/reports/exchange/mailbox-usage/export — Export report data