Microsoft is increasing Exchange Online mailbox storage for eligible Microsoft 365 Business licences as part of its 2026 pricing and packaging changes. For many organisations, the most noticeable improvement will be the increase in the standard mailbox limit from 50GB to 100GB.
If your business has users who are regularly receiving mailbox storage warnings, struggling to send email, or relying on frequent mailbox clean-ups to remain operational, this change could significantly reduce those day-to-day issues.
However, there are some important details to understand. The rollout is being completed gradually, not every Microsoft 365 tenant will receive the increase at the same time, and larger mailboxes do not remove the need for sensible mailbox management, archiving or backup.
Throughout this guide, we explain what is changing, who is affected, how to check whether your organisation has received the update, and what to do if users are already close to the current 50GB mailbox limit.
August 2026 Update: The 100GB mailbox rollout is still in progress
Since publishing this article, we have now assisted customers affected by Microsoft’s gradual rollout of the new 100GB mailbox limit.
Although Microsoft has begun increasing mailbox quotas for eligible Microsoft 365 Business tenants, the change is not appearing everywhere at the same time.
We recently worked with a customer whose mailbox had already reached the existing 50GB limit. Their tenant had not yet received the updated quota, despite the wider rollout being underway.
To keep email flowing without committing the customer to an unnecessary long-term licence upgrade, we temporarily enabled Exchange Online Archiving on a rolling monthly basis. Once Microsoft completes the rollout to their tenant, we will review whether the archive licence is still required.
Key point: Before upgrading Microsoft 365 licences simply to gain additional mailbox space, check whether your tenant has already received the new 100GB allocation.
Quick Summary
If you only have a minute, these are the main points:
- Eligible Microsoft 365 Business mailboxes are increasing from 50GB to 100GB.
- The rollout is gradual, so not every Microsoft 365 tenant will receive the increase at the same time.
- Businesses should check their current mailbox quota before buying additional licences purely for more storage.
- If a mailbox is already close to 50GB, Exchange Online Archiving can provide a practical interim solution.
- A larger mailbox does not remove the need for sensible archiving, retention, backup and mailbox management.
What is changing?
Microsoft 365 Business Basic, Business Standard and Business Premium currently include a 50GB primary Exchange Online mailbox for each licensed user.
As part of Microsoft’s 2026 Microsoft 365 pricing and packaging update, eligible Business plans are expected to receive an additional 50GB of primary mailbox storage. Once the rollout has completed, most users on eligible plans will have a 100GB primary mailbox instead of the current 50GB limit.
For many organisations, this is a welcome improvement. Users who regularly work with large volumes of email will have considerably more breathing room before reaching mailbox capacity, helping to reduce the risk of email disruption caused by full mailboxes.
However, businesses should remember that a larger mailbox does not remove the need for good mailbox management, sensible archiving policies or regular Microsoft 365 administration.
Microsoft 365 Is Changing in More Ways Than One
The mailbox increase isn't the only recent Microsoft 365 change. Microsoft 365 Copilot Chat is also now available at no additional cost with eligible business subscriptions.
Explore More Microsoft 365 Guidance
Visit the KES Microsoft 365 Learning Centre for practical guidance covering Exchange Online, Microsoft Teams, SharePoint, OneDrive, Microsoft Copilot, licensing, security and Microsoft 365 administration.
Visit the Microsoft 365 Learning Centre →Is the 100GB mailbox increase happening everywhere at the same time?
No. The Microsoft 365 pricing changes took effect from July 2026, but the associated packaging updates, including the additional Exchange Online mailbox storage, are being rolled out gradually.
This means businesses should not assume that every eligible mailbox will immediately show a 100GB quota. Microsoft 365 tenants may receive the change at different times, and administrators should check the actual mailbox quota rather than relying on the wider rollout announcement.
For organisations with users already close to the existing 50GB limit, this distinction is important. A user sitting at 49GB today could still experience sending or receiving problems before the new allowance reaches their tenant.
Microsoft 365 administrators should also keep an eye on the Microsoft 365 Message Center, where tenant-specific service and rollout information may be published.
Already close to 50GB? Don’t wait for the rollout.
If a mailbox is already approaching its current limit, waiting for Microsoft’s staged rollout may not be practical. Users can still be affected by sending or receiving restrictions until the new 100GB quota has actually been applied to their tenant.
Where immediate action is needed, Exchange Online Archiving can provide a practical interim option while the tenant waits for the new mailbox allowance.
What happens 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 may receive a warning that their mailbox is close to its storage limit.
At around 49.5GB, sending new email can become restricted until space is cleared.
At 50GB, the mailbox can be prevented from both sending and receiving email. Incoming messages may be rejected and the sender may receive a non-delivery report.
At that point, mailbox storage stops being a minor inconvenience and becomes a genuine business continuity issue. A user may be unable to send quotations, receive customer instructions, process orders, respond to suppliers or continue normal communication until the problem is resolved.
What will the increase mean for users currently nearing 50GB?
For users currently at 45GB, 48GB or just under the existing 50GB limit, the new allowance should make a significant difference once it has been applied to their Microsoft 365 tenant.
For example, a user with a 48GB mailbox today is using approximately 96% of their available mailbox capacity. If that same mailbox increases to 100GB, the user would immediately drop to around 48% utilisation.
That additional headroom should substantially reduce the immediate risk of sending or receiving restrictions caused purely by mailbox capacity.
However, it is still important to understand that a larger mailbox does not solve every underlying problem. It will not automatically address poor filing habits, oversized attachments, duplicated content, years of historic email, or Outlook performance issues.
Will users need to do anything?
In most cases, Microsoft will apply the mailbox increase automatically as part of the Microsoft 365 service update. Users should not normally need to recreate their mailbox, migrate their email or create a new Outlook profile simply to benefit from the larger quota.
However, Microsoft 365 administrators should take the opportunity to verify that the update has been applied correctly and that users who are already close to the existing limit are not left at risk.
We recommend checking the following:
- ✔ Confirm users are licensed with an eligible Microsoft 365 Business plan.
- ✔ Check the Microsoft 365 Message Centre for rollout notifications.
- ✔ Verify the mailbox quota has actually increased to 100GB.
- ✔ Review whether any mailboxes have customised quota settings applied.
- ✔ Identify users who are already close to, or over, the current 50GB limit.
- ✔ Review shared mailboxes, which are often overlooked but can also reach capacity.
If users are already at or above the current mailbox limit, waiting for Microsoft's rollout may not be practical. In these situations, temporary measures such as Exchange Online Archiving can help restore normal email use while waiting for Microsoft's staged rollout to complete.
Not sure whether your Microsoft 365 tenant has received the update?
KES can quickly review your Microsoft 365 environment, identify users approaching their mailbox limits, confirm whether the new 100GB quota has been applied, and recommend the most appropriate solution.
Whether you need temporary Exchange Online Archiving, licence advice or a wider Microsoft 365 health check, we'll help you choose the most cost-effective option rather than simply recommending unnecessary licence upgrades.
Many organisations upgrade Microsoft 365 licences purely because users are running out of mailbox space. With Microsoft's move to 100GB business mailboxes, some of those upgrades may no longer be necessary. Checking your tenant before changing licences could save unnecessary monthly subscription costs.
Choose the situation that best matches your Microsoft 365 environment
My mailbox is nearly full
Check the current mailbox quota in the Exchange Admin Centre and confirm whether your tenant has already received the new 100GB allocation.
Next step: Identify users above 45GB and monitor their mailbox growth closely.
My mailbox is already full
Do not rely on the rollout arriving in time. Immediate action may be needed to restore sending and receiving.
Next step: Consider Exchange Online Archiving or contact KES for help restoring normal email operation.
I'm not sure if we have received the update
Check the mailbox directly rather than assuming the new quota has been applied.
Next step: Open Exchange Admin Centre → Recipients → Mailboxes → Mailbox Usage and confirm whether the quota shows 50GB or 100GB.
We're reviewing Microsoft 365 generally
Mailbox storage is only one part of the wider Microsoft 365 environment. Licensing, backup, security, archiving and permissions should be reviewed together.
Next step: Review your Microsoft 365 configuration or speak to KES about a wider Microsoft 365 health check.
Need help deciding which option is right for your business?
Talk to KES About Microsoft 365 →What about Online Archive mailboxes?
The move to a 100GB primary mailbox does not replace Exchange Online Archiving. The two features solve different problems and can still work well together.
An Online Archive mailbox provides additional storage outside the user’s primary mailbox, allowing older email to remain accessible without consuming space in the main mailbox. This can be particularly useful for users with many years of historic email, large volumes of attachments or very fast mailbox growth.
For organisations waiting for Microsoft’s staged 100GB rollout, Exchange Online Archiving can also provide a practical short-term solution if a mailbox is already close to its current limit.
Even after the 100GB quota has been applied, archiving may still make sense for heavy email users. Simply doubling the size of the primary mailbox does not automatically solve long-term storage, retention or Outlook performance issues.
When does Exchange Online Archiving make sense?
- A mailbox is already close to 50GB and the 100GB rollout has not yet reached your tenant.
- A user has many years of historic email that still needs to remain searchable and accessible.
- Mailbox growth is unusually high and simply increasing the primary quota would only delay the problem.
- Outlook performance is becoming an issue because the primary mailbox contains a very large volume of email and attachments.
The right approach depends on how the mailbox is being used. In some cases, the new 100GB allowance may be sufficient. In others, archiving remains the better long-term option.
Will a larger mailbox improve Outlook performance?
Not necessarily.
Although increasing the primary mailbox from 50GB to 100GB provides considerably more storage, it does not automatically make Microsoft Outlook faster or more responsive.
Outlook performance is influenced by several factors, including the number of folders, the volume of messages, the size of attachments, the Outlook cache (OST file), search indexing, installed add-ins and the overall performance of the user's computer.
A user with a well-organised 80GB mailbox may experience excellent performance, while another user with a much smaller mailbox could still experience slow searches, delayed synchronisation or Outlook freezing if their profile or workstation has underlying issues.
For organisations with very large mailboxes, good mailbox housekeeping, sensible archiving policies and regular Microsoft 365 administration remain just as important as the additional storage Microsoft is providing.
The increase to 100GB should therefore be viewed as additional capacity rather than a performance upgrade.
A larger mailbox should not replace good mailbox management.
Even with 100GB available, businesses should continue to archive older email, remove unnecessary large attachments, review shared mailboxes and implement appropriate Microsoft 365 retention policies. Good housekeeping keeps Outlook responsive, simplifies administration and reduces long-term storage risks.
Final Thoughts
Microsoft's increase from 50GB to 100GB Exchange Online mailboxes is a welcome improvement for businesses using Microsoft 365. As the rollout progresses, users will benefit from additional storage, reducing the likelihood of mailbox capacity issues and giving organisations more flexibility when managing email.
However, larger mailboxes should not replace sensible mailbox management. Good retention policies, Microsoft 365 backup, Online Archive where appropriate, and regular administration remain essential for maintaining performance, compliance and business continuity.
If you're unsure whether your Microsoft 365 tenant has received the update, need advice on Exchange Online licensing, or would like help reviewing your Microsoft 365 environment, the KES team is here to help.
Which Microsoft 365 licences are affected?
The change applies to eligible Microsoft 365 Business plans, including Business Basic, Business Standard and Business Premium. Administrators should still verify the licence assigned to each user and confirm the quota shown in Exchange Online.
When will Microsoft increase my mailbox to 100GB?
Microsoft is rolling the change out gradually rather than switching every eligible Microsoft 365 tenant at the same time. Some businesses may already see the new 100GB quota, while others may still be waiting. The safest approach is to check the actual mailbox quota in the Exchange Admin Centre rather than assume the increase has already been applied.
Do I need to enable the larger mailbox?
In most cases, no manual migration or mailbox recreation should be required. Microsoft is applying the change as part of the service rollout. However, administrators should still confirm that the mailbox quota has actually increased.
How can I check whether a mailbox has increased to 100GB?
Open the Exchange Admin Centre, go to Recipients → Mailboxes, select the user and review Mailbox Usage. This will show whether the primary mailbox is still limited to 50GB or has increased to 100GB.
What happens if a mailbox reaches 50GB before the rollout arrives?
Users may begin receiving storage warnings as they approach the current limit, and sending or receiving email can eventually be restricted. If the mailbox is already very close to capacity, waiting for the rollout may not be practical. Exchange Online Archiving can provide a useful interim option.
Should I still use Exchange Online Archiving after the mailbox increases?
Possibly. Online Archive remains separate from the primary mailbox and can still be useful for users with many years of historic email, large volumes of attachments or consistently high mailbox growth. The right approach depends on how the mailbox is being used.
Will a 100GB mailbox make Outlook faster?
Not necessarily. The larger quota provides more storage, but Outlook performance is also affected by factors such as OST file size, number of folders, number of items, add-ins, device performance and cached mode settings. A larger mailbox should be viewed as extra capacity rather than a performance upgrade.
Do I still need Microsoft 365 backup?
Yes. Mailbox capacity and backup are separate issues. A larger mailbox gives users more storage but does not provide additional protection against accidental deletion, retention changes, malicious activity or other forms of data loss.
Should I upgrade a Microsoft 365 licence just because a mailbox is nearly full?
Not automatically. If the only reason for upgrading is additional mailbox space, check whether the tenant has already received the new 100GB quota first. Licence decisions should also consider security, compliance, archiving, retention and other features the user may depend on.
What should I do if I am not sure which option is right?
Start by checking the current mailbox quota, licence assignment and mailbox usage. If the mailbox is already close to capacity, it may be worth reviewing Exchange Online Archiving, Outlook performance and the wider Microsoft 365 configuration before making licence changes.
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