Understanding the new 100 GB mailbox entitlement for Microsoft 365 Business suites

Microsoft 365 Business Basic, Business Standard, and Business Premium now include an additional 50 GB of primary email storage for eligible users. This brings the supported primary mailbox entitlement from 50 GB to a maximum of 100 GB. We wanted to talk about this change, so Exchange Online administrators understand how this mailbox size increase is delivered. We will focus only on mailbox size in this post.

What changed for the Business suites

Microsoft announced an additional 50 GB of email storage for Microsoft 365 Business Basic, Business Standard, and Business Premium as part of the 2026 Microsoft 365 packaging updates. The packaging changes are rolling out June - September 2026, with customers receiving advance notice through Message Center before the changes became available in their tenant.

The additional storage changes the effective primary mailbox size for eligible Business suite users from 50 GB to 100 GB. The affected commercial product suites are:

• Microsoft 365 Business Basic
• Microsoft 365 Business Standard
• Microsoft 365 Business Premium

After the rollout, all users that had the appropriate licenses assigned will have received a new service plan and the corresponding mailbox quota increase.

Please note: this mailbox size increase applies only to the above-mentioned suite licenses; there can still be licenses (such as standalone Exchange Online Plan 1) that have the maximum mailbox size set at 50 GB.

The supported quota outcome

The additional storage establishes a maximum effective quota of 100 GB for the eligible Business suite scenario.

• A user whose highest applicable Exchange mailbox plan is the Business suite plan receives an effective 100 GB quota when the storage add-on is present.
• A user who also has an Enterprise or standalone Exchange license that already provides a 100 GB mailbox remains entitled to 100 GB.
• A user who has multiple licenses assigned, which contain multiple Exchange service plans (this is known as Concurrent Licensing), will be granted the maximum quota provided by a single product – the quotas are not additive across products. For example, a user with one of the Business Suite and a separate Enterprise license containing Exchange Online Plan 2, will still be entitled to 100 GB. The quota increase for the Business suites affects the base mailbox size only. It does not provide archive capabilities.

How the additional quota is implemented

The Business suite provides the total storage through a combination of service plans:

• The Business suite Exchange plan is represented by BPOS_S_STANDARD, which grants 50 GB of storage.
• The additional entitlement is represented by the EXCHANGE_STORAGE_50GB service plan, which adds +50 GB, increasing the total quota to 100 GB.

Both plans must be enabled for the user to have the full 100 GB.

In your Microsoft 365 admin center, this will look like the following – there is a “standard” license and there is an add-on:

 

Custom mailbox quotas are preserved

If an administrator has configured a custom mailbox quota, the additional storage logic does not overwrite that setting. Likewise, removing the add-on does not replace a later administrator-defined custom value. This protects deliberate tenant-level mailbox management choices.

For example, if an administrator configured the mailbox for user with a Business suite from the original default of 50 GB down to 20 GB, the user’s quota will remain at 20 GB even after the additional service plan is assigned to them.

Reviewing the user’s licenses and service plans

In the Microsoft 365 admin center, open Users > Active users, select the user, and review Licenses and apps. Confirm that the user has an eligible Microsoft 365 Business suite and that its included services are enabled. The Billing > Licenses page can also show whether the product was assigned directly or through group-based licensing.

Microsoft Graph PowerShell can provide a more detailed service-plan view. The following example retrieves the assigned license details and searches for the storage service plan:

$licenses = Get-MgUserLicenseDetail -UserId user@contoso.com
$licenses.ServicePlans | Where-Object ServicePlanName -eq "EXCHANGE_STORAGE_50GB" | Select-Object ServicePlanName, ProvisioningStatus

Review the effective Exchange mailbox quota

Exchange Online PowerShell shows the quota values that Exchange presents for the mailbox. For example:

Get-Mailbox -Identity user@contoso.com | Format-List IssueWarningQuota, ProhibitSendQuota, ProhibitSendReceiveQuota, UseDatabaseQuotaDefaults

For an eligible Business suite user with the additional storage service plan and no custom quota, the effective maximum mailbox quota should be 100 GB.

Common license and quota scenarios

• Business suite with the +50 GB storage add-on: user’s effective primary mailbox maximum is 100 GB.
• Business suite without the +50 GB storage add-on: base Business mailbox quota continues to apply until the additional service plan is provisioned (should happen automatically).
• Business suite plus an Enterprise or standalone plan that already grants 100 GB: effective maximum remains 100 GB because Exchange uses the highest applicable entitlement rather than adding the quotas.
• Business suite plus a lower Exchange capability (for example, F3 license): Business plan remains the highest capability, so the add-on can raise the effective maximum to 100 GB.
• Custom quota: administrator-defined values remain in effect and are not replaced by the automatic +50 GB boost.
• +50 GB add-on explicitly removed: for a mailbox using default plan quotas, Exchange returns to the applicable plan default. A custom value set by an administrator remains custom.

Rollout and license propagation

The additional storage is represented through licensing data, so the service plan must be assigned and processed before Exchange can return the higher effective quota. During broad service-plan rollout or backfill operations, users in the same organization may not all reflect the change at the same time. It is possible that some of your users received additional 50 GB mailbox size increase while others did not – you should expect that this gets resolved automatically if users are licensed by one of affected business suite licenses.

Administrators should not remove and reassign an Exchange license solely to force a quota refresh unless Microsoft Support specifically directs that action. Removing a product license removes access to its services and starts the applicable data-retention lifecycle. Please keep using your normal license-assignment processes.

Exchange Online Team