Microsoft Doubles Mailbox Storage to 100 GB for Exchange Online Users

Key Takeaways

• Microsoft has doubled the primary mailbox storage for eligible Exchange Online users.
• Users on Microsoft 365 Business Basic, Business Standard, and Business Premium plans now receive 100 GB, up from 50 GB.
• This increase is part of Microsoft’s 2026 packaging updates, rolling out between June and September.
• The additional capacity applies only to primary mailboxes and does not include archive features or stack with other licenses.

Microsoft has initiated a significant expansion of primary mailbox storage for its Exchange Online users, specifically targeting those subscribed to Microsoft 365 Business Basic, Business Standard, and Business Premium plans. This update effectively doubles the previous 50 GB entitlement, providing eligible users with a robust 100 GB of mailbox capacity.

This enhancement is a component of Microsoft’s broader 2026 packaging adjustments, which commenced in June and are slated for completion by September. Prior to the rollout of these service plan modifications, Microsoft communicated the impending changes to tenant administrators via the Message Center.

It is crucial for administrators to understand that this increased capacity is exclusively for the primary mailbox. It does not automatically extend to archive mailbox functionalities, compliance features, or other benefits typically associated with Exchange Online Plan 2.

Microsoft Expands Mailbox Storage

The new 100 GB entitlement is delivered through a combination of two Exchange-related service plans. The original 50 GB quota is provisioned by the existing BPOS_S_STANDARD service plan, while an additional 50 GB is added via a new service plan identified as EXCHANGE_STORAGE_50GB.

For a user to receive the full 100 GB primary mailbox quota, both of these service plans must be enabled. This additional capacity is integrated directly into the user’s primary Exchange mailbox limit; it is not provided as a separate mailbox or as supplementary archive storage.

Administrator Verification

Administrators can confirm the assigned plans within the Microsoft 365 admin center by navigating to Users > Active users > Licenses and apps. The presence of the new storage service plan can also be verified using Microsoft Graph PowerShell with the following command:

$licenses = Get-MgUserLicenseDetail -UserId [email protected]
$licenses.ServicePlans | Where-Object ServicePlanName -eq "EXCHANGE_STORAGE_50GB" |
Select-Object ServicePlanName, ProvisioningStatus

This storage increase is specifically for Microsoft 365 Business Basic, Business Standard, and Business Premium subscribers. Standalone Exchange Online Plan 1 licenses will continue to maintain a 50 GB primary mailbox limit.

Understanding Licensing and Quotas

Organizations that assign multiple Exchange licenses to a single user should note that storage quotas are not cumulative. Exchange Online operates on a principle where the user receives the highest mailbox entitlement available from any single applicable product license. For instance, a user with both a Business Premium license and an Exchange Online Plan 2 or Microsoft 365 E3 license will still be capped at 100 GB, rather than receiving a combined 200 GB. This aligns with Microsoft’s concurrent licensing model, which allows for multiple service plans but does not stack mailbox capacity beyond the maximum supported entitlement.

Microsoft confirmed that the automatic increase in storage will not override any mailbox quotas previously defined by an administrator. If an administrator had manually reduced a mailbox quota from 50 GB to 20 GB, it will remain at 20 GB even after the new add-on service plan is provisioned. Similarly, removing the new storage service plan will not alter a subsequent custom quota. This behavior is designed to preserve tenant-specific mailbox governance and retention policies.

To inspect the effective Exchange quota, administrators can use Exchange Online PowerShell:

Get-Mailbox -Identity [email protected] |
Format-List IssueWarningQuota,ProhibitSendQuota,ProhibitSendReceiveQuota,UseDatabaseQuotaDefaults

For an eligible user with both service plans enabled and no manually configured quota, the effective maximum should display as 100 GB.

Due to the dependency on the provisioning of licenses and service plans, users within the same tenant may not experience the new quota simultaneously. Microsoft expects the process to complete automatically for all properly licensed users within the June-to-September rollout window. Administrators are advised against removing and reassigning Exchange licenses in an attempt to force a quota refresh, as this action can disrupt service access and trigger the associated data-retention lifecycle. Instead, organizations should adhere to standard license-assignment procedures and verify the presence of the new storage plan.

What You Should Do

• Verify User Entitlements: Use the Microsoft 365 admin center or PowerShell commands provided to confirm that eligible users have received the EXCHANGE_STORAGE_50GB service plan.
• Communicate Changes: Inform your end-users about the increased mailbox capacity, especially those who may have been managing near-full mailboxes.
• Review Custom Quotas: If your organization implements custom mailbox quotas, be aware that the automatic increase will not override these. Adjust custom quotas as needed to leverage the new default capacity.
• Avoid Manual License Reassignment: Do not remove and reassign Exchange licenses to expedite the quota update, as this can lead to service interruptions and data retention issues. Allow the automatic rollout process to complete.
• Monitor Rollout Progress: Keep an eye on the Message Center for any further updates from Microsoft regarding the completion of the rollout.

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