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Summary: Eligible Business users don’t need to manually increase Office 365 mailbox size from 50 GB to 100 GB. From 1 July 2026, Microsoft has increased the primary mailbox storage quota to 100 GB per user for Business tenants. However, it may take some time to take effect on every user or tenant; you must check your mailbox size limit from the Exchange Admin Center (EAC).
A mailbox that is close to its storage limit can cause problems with sending and receiving emails. If you are searching for how to increase Office 365 mailbox size to 100 GB, you don’t need to worry now. Microsoft has changed the storage entitlement for eligible Microsoft 365 Business plans.
As part of Microsoft’s 2026 commercial licensing update, eligible Microsoft 365 Business Basic, Business Standard, and Business Premium users are being moved from a 50 GB to a 100 GB primary mailbox entitlement. Microsoft says the rollout may take time to appear across all tenants.
Office 365 Mailbox Size Limits: Primary & Archive Mailbox
Your Microsoft 365 license and mailbox configuration determine the available primary mailbox storage. As per the July 2026 update, Microsoft’s Business plan has the following mailbox limits:
| Microsoft 365 plan | Primary mailbox | Archive mailbox |
|---|---|---|
| Business Basic | 100 GB* | 50 GB |
| Business Standard | 100 GB* | 50 GB |
| Business Premium | 100 GB* | 1.5 TB |
| Enterprise E3 | 100 GB | 1.5 TB |
| Enterprise E5 | 100 GB | 1.5 TB |
| Exchange Online Plan 1 | 50 GB | 50 GB |
| Exchange Online Plan 2 | 100 GB | Eligible for larger archive capacity |
Note: This update applies to eligible user mailboxes. Shared and resource mailboxes have separate licensing and storage rules.
Has Microsoft Increased the Office 365 Mailbox Size to 100 GB?
Yes. Microsoft has increased the primary mailbox storage limits for eligible Microsoft 365 Business Basic, Business Standard, and Business Premium users from the 50 GB limit to 100 GB.
In July 2026, Microsoft confirmed that users who only require a 100 GB primary mailbox can continue using these Business licenses and do not need Exchange Online Plan 2 solely to obtain additional primary mailbox capacity. As a very important note, Microsoft also clarified that the rollout may not appear immediately for every tenant. For eligibility, you need to check your storage quota.
Note: Still, there is a possibility that you may see older limits for some Microsoft 365 plans or Business plans while the licensing change is being rolled out. Therefore, verify the actual quota assigned to a mailbox before changing licenses.
How to Check Your Office 365 Mailbox Size: Step-by-Step Guide
In the Exchange Admin Center, you can check the actual storage limit assigned to the user. For that, follow the steps below:
- Sign in to the Exchange admin center with admin credentials.
- Go to Recipients and tap on Mailboxes.
- Select the user mailboxes for whose mailbox size you need to check and double-click on that.
- Now review the mailbox usage and quota information.
You must check the mailbox storage quota because the entitlement may not be visible in every tenant at the same time. From now on, check the mailbox quota first from now before you make changes or upgrade the Microsoft 365 subscription.
What Happens When an Office 365 Mailbox Reaches its Limit?
Mailbox storage quotas consist of three limits, namely warning limits, send limit, and send/receive limit. When a mailbox space tends to be full, you may get warnings to have some more space. Once applicable sending and receiving limits are reached, even email functionality can be affected. Depending on the quota state, you may:
- Receive mailbox storage warnings
- Be unable to send new emails
- Be unable to receive new emails
- Receive non-delivery reports for messages sent to a full mailbox
- Experience interruptions to normal email communication
The important point is that these limits are based on the mailbox’s assigned quota, not simply an old 50 GB rule.
What If Your Mailbox is Still Full After Getting 100 GB?
Increasing mailbox capacity is not always the best way to opt for. Organizations may also need to retain older email for compliance, migration, backup, or other business requirements. If you need an offline copy of Office 365 mailbox data, you can export Office 365 mailbox to PST.
However, Microsoft provides native options, from Export PST to retention policies to keep data safe and back up mailbox data as well. But for more quick, automated, as well as scheduled export, you can opt for Kernel Export Office 365 to PST software. Having Office mailbox data in PST can be useful when email data needs to be retained or moved again. You can also export Office 365 mailbox data in PDF and other useful formats to fulfill your different kinds of needs.
Conclusion
Now, after July 2026, with Microsoft’s 2026 mailbox-storage update, the answer to how to increase mailbox size in Office 365 has changed. There is no need to upgrade to an Enterprise plan because eligible Microsoft 365 Business Basic, Business Standard, and Business Premium users can now have up to 100 GB of primary mailbox storage.
You just need to check the actual mailbox quota in the Exchange Admin Center. If the mailbox remains at 50 GB instead of the 100 GB quota, review the tenant’s licensing and rollout status. Moreover, for users who still need to reduce mailbox usage, export Office 365 mailbox data to PST and keep it safe to fulfill further needs.
Frequently Asked Questions
A: Yes, but if you’re eligible for Microsoft 365 Business Basic, Business Standard, and Business Premium, you may now have a predefined 100 GB primary mailbox. You don’t need to increase it manually. However, Microsoft’s rollout may take time to reach every tenant.
A: Not solely for the 100 GB primary mailbox. If you have an eligible Business Basic, Standard, or Premium license with the updated entitlement you’ve already have a 100 GB mailbox size.
A: No. An archive mailbox is separate from the primary mailbox. It can help move older data out of the primary mailbox and reduce its storage usage.
