Microsoft 365 Business Mailbox Storage Is Increasing: What the July 2026 Change Means for Users Nearing 50GB

Microsoft is making an important change to Microsoft 365 Business email storage as part of its 2026 pricing and packaging update. For many organisations, the most noticeable change will be the addition of extra Exchange Online mailbox storage for eligible Microsoft 365 plans.

This is particularly relevant for businesses with users who are already close to the current 50GB mailbox limit. If you have staff regularly receiving mailbox warnings, struggling to send email, or relying on manual clean-ups to stay under the limit, this change could provide some much-needed breathing room.

However, it is important to understand how the change will work, when it is expected to apply, and why it does not completely remove the need for good mailbox management.

What is changing?

Microsoft 365 Business Basic, Business Standard and Business Premium currently include a 50GB primary mailbox for each licensed user.

As part of Microsoft’s 2026 packaging update, eligible Microsoft 365 Business plans are expected to receive an additional 50GB of Exchange Online mailbox storage. In practical terms, this means many business users who currently have a 50GB primary mailbox limit should move to a 100GB primary mailbox limit once the change has been applied to their tenant.

For many small and medium-sized businesses, this is a positive change. It reduces the pressure on users who have large mailboxes and helps avoid situations where email stops working simply because a user has hit the 50GB ceiling.

If you want to understand Microsoft 365 in more detail, visit our Microsoft 365 Learning Centre, where we cover practical Microsoft 365 guidance for businesses.

Is the change happening exactly on 1 July 2026?

Not necessarily.

The Microsoft 365 commercial pricing changes are due to take effect from 1 July 2026. However, the related packaging updates, including the additional mailbox storage, are being rolled out during the summer period.

This means businesses should not assume that every mailbox will automatically show a 100GB quota on the morning of 1 July. Microsoft has indicated that eligible tenants should receive advance notice through the Microsoft 365 Message Center before the packaging changes become available.

For organisations with users already sitting close to 50GB, this distinction matters. A user who is currently at 49GB or above could still run into problems before the new allowance is applied.

What happens today when a mailbox gets close to 50GB?

Under the current Exchange Online mailbox limits, Microsoft applies several thresholds as a mailbox approaches capacity.

At around 49GB, the user receives a warning that their mailbox is approaching its limit.

At around 49.5GB, the user may be prevented from sending new email until space is cleared.

At 50GB, the mailbox can be blocked from both sending and receiving email. Incoming messages may be rejected, and the sender may receive a non-delivery report.

This is where mailbox storage stops being a minor inconvenience and becomes a real business continuity issue. A user may be unable to send quotes, receive customer instructions, process orders, respond to suppliers, or continue normal communication until the problem is resolved.

What will this mean for users currently nearing 50GB?

For users currently at 45GB, 48GB or just under 50GB, the new allowance should make a significant difference once it is applied.

For example, a user with a 48GB mailbox today is using approximately 96% of their available mailbox capacity. If that user’s mailbox limit increases to 100GB, the same mailbox would be using around 48% of its available capacity.

That gives the user far more breathing room and should reduce the immediate risk of being blocked from sending or receiving email.

However, it is not a reason to ignore mailbox growth completely. A larger mailbox gives users more space, but it does not automatically fix poor filing habits, large attachments, duplicated content, historic email build-up, or Outlook performance issues.

Will users need to do anything?

In most cases, the increase should be applied by Microsoft as part of the service update, provided the user is on an eligible Microsoft 365 plan.

Users should not normally need to recreate their mailbox, migrate their email, or set up a new Outlook profile purely to benefit from the larger quota.

That said, Microsoft 365 administrators should still check the following:

Whether users are on eligible Microsoft 365 Business licences.
Whether the tenant has received the relevant Microsoft 365 Message Center notification.
Whether the mailbox quota has actually changed in Exchange Online.
Whether any mailboxes have manually customised quota settings.
Whether any users are already blocked from sending or receiving email.

If a user is already at or above the current limit, waiting for the Microsoft rollout may not be practical. The business may need to take short-term action to restore normal email use before the new quota becomes available.

KES can help review mailbox usage, licence assignments and tenant settings through our managed Microsoft 365 support service.

What about Online Archive mailboxes?

The mailbox storage increase relates to the primary Exchange Online mailbox. This is separate from Online Archive storage.

An Online Archive mailbox can still be a useful way to move older email out of the primary mailbox while keeping it accessible to the user. This can be particularly helpful for users with many years of historic email or very large volumes of stored messages.

The move from 50GB to 100GB will reduce pressure on the primary mailbox, but it should not automatically replace good archiving and retention practices.

For example, if a user has 10 years of email, thousands of large attachments, and no meaningful filing structure, giving them another 50GB may only delay the problem. It does not necessarily solve the underlying issue.

Will the larger mailbox improve Outlook performance?

Not automatically.

A larger cloud mailbox quota does not mean Outlook will suddenly become faster on the user’s device. Outlook performance can be affected by several factors, including mailbox size, number of folders, number of items in key folders, cached mode settings, OST file size, device performance, add-ins and network quality.

In some cases, users with very large mailboxes may still experience slow search, delayed synchronisation or general Outlook sluggishness even when they are comfortably within the Microsoft 365 storage limit.

For heavy mailbox users, it is still sensible to review Outlook caching settings, archive older content where appropriate, and avoid keeping excessive numbers of items in core folders such as Inbox and Sent Items.

Does this remove the need for mailbox housekeeping?

No.

The additional storage is helpful, but it should not be treated as permission to store everything forever in the primary mailbox.

Businesses should still think carefully about how email is being used. In particular, they should consider:

Deleting unnecessary email and large attachments.
Moving older email into archive mailboxes where appropriate.
Reviewing retention policies.
Checking shared mailboxes as well as user mailboxes.
Identifying users with unusually high mailbox growth.
Encouraging users to store business documents in SharePoint or OneDrive rather than using email as a filing system.

A mailbox is not a substitute for proper document storage, retention planning or backup. If your business relies heavily on Microsoft 365, it is also worth reviewing whether your email, files and Teams data are protected by a dedicated Microsoft 365 backup solution.

What should businesses do before the change?

The best approach is to audit mailbox usage now rather than waiting until users hit the limit.

Businesses should identify users who are already above 45GB, users whose mailboxes are growing quickly, and users who have previously received storage warnings. These are the people most likely to be affected before the new allowance is fully rolled out.

For each user, the right action may be different. Some may only need a short-term clean-up. Some may benefit from Online Archive. Some may need their Outlook cache settings reviewed. Others may need a wider conversation about how they store files, attachments and long-term business records.

It is also worth reviewing shared mailboxes. Shared mailboxes are often overlooked because they are not always tied to a named user, but they can still hit storage limits and disrupt business processes.

Should businesses cancel licence upgrades or archive plans?

Not automatically.

If a user was upgraded purely because they needed more than a 50GB mailbox, the new allowance may change the licensing conversation. However, licensing should never be changed based on mailbox size alone.

A higher licence may also provide other features, such as additional security, compliance, archiving, retention, device management or identity protection. Removing or downgrading a licence without checking the full dependency could create new problems elsewhere.

Before making licence changes, businesses should review what each user actually needs and which Microsoft 365 features are currently in use.

Do businesses need to review Microsoft 365 security at the same time?

This is a sensible time to do so.

Mailbox storage, licensing, archiving and security are closely connected. If you are already reviewing Exchange Online and Microsoft 365 settings, it makes sense to also check key security controls such as multi-factor authentication, mailbox permissions, shared mailbox access, administrator roles and external forwarding rules.

For organisations that want a more structured review, KES offers Microsoft 365 security hardening to help improve Microsoft 365 security configuration and reduce common risks.

The key takeaway

Microsoft’s additional Exchange Online mailbox storage is a welcome change for Microsoft 365 Business users, especially those currently close to the 50GB limit.

For users at 45GB or above, the move to a larger mailbox should significantly reduce the immediate risk of being blocked from sending or receiving email once the new quota is applied.

However, businesses should not simply wait and hope the issue resolves itself. Users already near the current limit remain at risk until the new quota is visible in the tenant. Mailbox size, archiving, Outlook performance, licensing and backup should all be reviewed as part of the wider Microsoft 365 management process.

The increase gives businesses more breathing room. It does not remove the need for good email management.

Need help checking which users are close to their mailbox limits?

KES can review your Microsoft 365 tenant, identify users at risk, check mailbox quotas, review licensing and advise whether archiving, backup or Microsoft 365 management changes are needed.

Learn more about our managed Microsoft 365 support or browse our Microsoft 365 Learning Centre for more practical guidance.

Microsoft 365 Business Mailbox Limit Increasing to 100GB: What Businesses Need to Know