Microsoft has started expanding primary mailbox storage for Microsoft 365 Business Basic, Business Standard, and Business Premium users. Eligible users can now receive up to 100 GB of Exchange Online mailbox capacity, doubling the previous 50 GB entitlement.
The change is part of Microsoft’s 2026 packaging updates, which began rolling out in June and are expected to continue through September. Microsoft also issued advance tenant notifications through the Message Center before the service-plan changes became available.
The increased capacity applies only to the primary mailbox. It does not automatically provide archive mailbox features, compliance capabilities, or other benefits of Exchange Online Plan 2.
Microsoft Expands Mailbox Storage
Microsoft delivers the new 100 GB entitlement through two Exchange-related service plans. The existing BPOS_S_STANDARD service plan provides the original 50 GB quota. A new EXCHANGE_STORAGE_50GB service plan adds another 50 GB.
Both service plans must be enabled for an eligible user to receive the full 100 GB primary mailbox quota. The added capacity is not a separate mailbox or additional archive storage it is an increase to the user’s primary Exchange mailbox limit.
Administrators should verify the assigned plans in the Microsoft 365 admin center under Users > Active users> Licenses and apps. The storage service plan may also be reviewed using Microsoft Graph PowerShell:
$licenses = Get-MgUserLicenseDetail -UserId [email protected]
$licenses.ServicePlans | Where-Object ServicePlanName -eq "EXCHANGE_STORAGE_50GB" |
Select-Object ServicePlanName, ProvisioningStatusThe change is limited to Microsoft 365 Business Basic, Business Standard, and Business Premium. Standalone Exchange Online Plan 1 licenses can still retain a 50 GB primary mailbox limit.
Organizations assigning multiple Exchange licenses to one user should note that storage quotas are not cumulative. Exchange Online offers the highest mailbox entitlement available in a single applicable product.
For example, a user assigned Business Premium and an Exchange Online Plan 2 or Microsoft 365 E3 license remains capped at 100 GB, rather than receiving 200 GB.
This follows Microsoft’s concurrent licensing model, where multiple service plans can be assigned. However, mailbox capacity does not stack beyond the highest supported entitlement.
Microsoft confirmed that the automatic storage increase will not overwrite administrator-defined mailbox quotas. If an administrator previously reduced a mailbox quota from 50 GB to 20 GB, it will remain at 20 GB after the add-on service plan is provisioned.
Likewise, removing the new storage service plan does not replace a later custom quota. This behavior protects tenant-specific mailbox governance and retention practices.
Administrators can inspect the effective Exchange quota with Exchange Online PowerShell:
Get-Mailbox -Identity [email protected] |
Format-List IssueWarningQuota,ProhibitSendQuota,ProhibitSendReceiveQuota,UseDatabaseQuotaDefaultsFor an eligible user with both service plans enabled and no manually configured quota, the effective maximum should show 100 GB.
Because the update depends on provisioning of licenses and service plans, users within the same tenant may not receive the new quota simultaneously.
Microsoft says the process should complete automatically for properly licensed users during the June-to-September rollout window. Administrators should avoid removing and reassigning Exchange licenses to force a quota refresh.
License removal can interrupt service access and trigger the associated data-retention lifecycle. Instead, organizations should continue with standard license-assignment processes and verify that the new storage plan is in place.
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