The highly anticipated Microsoft 365 mailbox storage increase is finally here, and it instantly resolves one of the most frustrating helpdesk tickets: running out of primary email space. Consequently, Microsoft is expanding the primary Exchange Online mailbox capacity for eligible Business Basic, Business Standard, and Business Premium users.
This guide details the exact rollout timeline, how the backend service plans work, and the commands needed to verify the new 100 GB entitlement without disrupting custom quotas.
Let’s examine the actual numbers:
The server-side rollout began in June 2026 and continues through September. Microsoft is doubling the previous 50 GB entitlement to a 100 GB primary mailbox quota. IT administrators have received advance tenant notifications via the Message Center regarding this free capacity boost. If your organization also manages on-premise Exchange environments, verify your servers are updated against recent threats using our Exchange Server Zero-Day Patch Guide.
This specific Microsoft 365 mailbox storage increase applies exclusively to the primary mailbox. Enterprise-tier archive features, compliance retention capabilities, and other benefits exclusive to Exchange Online Plan 2 require separate licensing.
How Does the Microsoft 365 100GB Mailbox Storage Increase Work?
The Microsoft 365 mailbox storage increase works by combining the original BPOS_S_STANDARD service plan (50 GB) with a newly provisioned EXCHANGE_STORAGE_50GB add-on service plan. Both plans must be actively enabled on an eligible user’s account to successfully deliver the 100 GB maximum primary mailbox quota.
The added capacity functions as a direct expansion of the primary Exchange mailbox limit. It is not a secondary archive.
Here is the inconvenient truth:
Concurrent licensing quotas do not stack in Microsoft 365. When a user is assigned multiple Exchange licenses, Exchange Online provisions the highest single mailbox entitlement available across all assigned products. A user with both Business Premium and Exchange Online Plan 2 remains capped at 100 GB total.
How to Check Exchange Service Plans via PowerShell?
To check Exchange service plans via PowerShell, IT administrators can utilize the Microsoft Graph PowerShell module by running the Get-MgUserLicenseDetail command. This command queries the specific user ID and filters the ServicePlans property to verify if the EXCHANGE_STORAGE_50GB add-on is actively provisioned.
Administrators should proactively verify assigned plans inside the Microsoft 365 admin center under Users > Active users > Licenses and apps. Alternatively, you can use the Microsoft Graph PowerShell module by running these two commands in sequence:
- First, fetch the user’s licenses:
$licenses = Get-MgUserLicenseDetail -UserId user@contoso.com - Next, filter for the storage plan:
$licenses.ServicePlans | Where-Object ServicePlanName -eq "EXCHANGE_STORAGE_50GB" | Select-Object ServicePlanName, ProvisioningStatus
Will Custom Mailbox Quotas Remain Safe After the 100GB Update?
Yes, custom mailbox quotas will remain completely safe after the 100GB update. The automatic backend storage increase respects manually configured administrator quotas. If a mailbox was previously restricted to 20 GB, it will remain at 20 GB even after the new 50 GB storage add-on is provisioned.
This behavior protects tenant-specific data retention and storage policies from backend update disruptions.
To inspect a user’s effective Exchange quota without impacting their workflow, run this Exchange Online PowerShell command:
- Check quota limits:
Get-Mailbox -Identity user@contoso.com | Format-List IssueWarningQuota, ProhibitSendQuota, ProhibitSendReceiveQuota, UseDatabaseQuotaDefaults
You should never remove licenses to force a quota refresh because stripping an Exchange license temporarily severs a user’s email access and triggers irreversible data-retention lifecycle deletions.
| License Setup Scenario | Required Service Plans | Effective Maximum Quota |
|---|---|---|
| Business Basic / Standard | BPOS_S_STANDARD + EXCHANGE_STORAGE_50GB | 100 GB |
| Suite + Exchange Plan 2 | Highest single applicable plan | 100 GB (No stacking) |
| Custom Admin Quota | BPOS_S_STANDARD + EXCHANGE_STORAGE_50GB | 20 GB (Retains custom value) |
Official Microsoft Documentation:Understanding the new 100 GB mailbox entitlement for Microsoft 365 Business
FAQ: Microsoft 365 Mailbox Storage Increase
Does the Microsoft 365 mailbox storage increase include archive storage?
No. The storage increase from 50 GB to 100 GB applies exclusively to the primary Exchange mailbox limit. Archive features require separate Enterprise or Plan 2 licensing.
When will my tenant receive the 100GB quota?
The automated provisioning rollout spans from June 2026 through September 2026. Users within the same tenant may receive the update at different times as the backend synchronizes.
What happens if a user holds both Business Premium and Exchange Online Plan 2?
The quotas do not stack. Exchange Online will provision the highest single mailbox entitlement available, meaning the user will remain capped at a 100 GB primary mailbox.
Do I need to manually assign the EXCHANGE_STORAGE_50GB add-on?
No, the add-on is provisioned automatically by Microsoft. IT administrators should simply wait for the sync to complete and avoid manually removing licenses to force a refresh.
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