Microsoft has doubled the primary mailbox limit on Microsoft 365 Business Basic, Business Standard and Business Premium, from 50 GB to 100 GB. The rollout was scheduled to finish by the end of September, so your tenant should already have it, and you don’t need to change plan or buy anything.
For most businesses, this is a quiet improvement. There’s usually a small group who’ve been living near the 50 GB ceiling for years: founders, account directors, anyone who’s never deleted a sent item and swaps 40 MB pitch decks with clients every week. They now have twice the room. How Microsoft has delivered the extra space has a few quirks, though, and if you’ve been buying extra Exchange licences to get round the old limit, some of that spend may now be unnecessary.
How the extra 50 GB is delivered
Microsoft hasn’t touched the existing Exchange plan inside the Business suites. That plan, which appears in licence details as BPOS_S_STANDARD, still grants 50 GB. The extra 50 GB comes from a second service plan, EXCHANGE_STORAGE_50GB, which Microsoft has been adding to every Business licence since June. A user needs both plans switched on to reach 100 GB.
That second plan is easy to switch off by accident. Licence tidy-ups often involve unticking service plans that nobody recognises, and a new item with a name like that is a prime candidate. If someone’s mailbox still shows 50 GB, it’s the first thing we’d check.
What stays the same
If you’ve set a custom quota on a mailbox, Microsoft leaves it alone. That applies whether you’ve raised a limit or deliberately lowered one, so any mailbox you’ve capped won’t jump to 100 GB on its own.
Quotas also don’t add together. Exchange uses the highest entitlement a user has from any single licence, so someone with Business Premium and Office 365 E3 still gets 100 GB.
The increase only applies to the primary mailbox. It doesn’t add any archive capacity or the compliance features that come with Exchange Online Plan 2. Business Premium keeps the archiving it already includes.
Standalone Exchange Online Plan 1 stays at 50 GB. If you have a few users on that licence for shared or low-use accounts, nothing changes for them.
| User's licenses | Effective primary mailbox limit |
|---|---|
| Business Basic, Standard or Premium, both Exchange plans on | 100 GB |
| Business suite with the extra storage plan switched off | 50 GB |
| Business suite plus E3 or Exchange Online Plan 2 | 100 GB (no stacking) |
| Standalone Exchange Online Plan 1 | 50 GB |
| Any licence with a custom quota set by an admin | Whatever the admin set |
Licenses worth reviewing at renewal
Until now, the usual fix for a full mailbox on a Business plan was to add Exchange Online Plan 2 to that user or move them onto an Enterprise licence. If extra space was the only reason, you may be able to remove it at your next renewal, which will help soak up some of July’s Microsoft price rises.
Check what else that licence is doing first. Exchange Online Plan 2 also brings larger archives and features such as litigation hold, and those might be the real reason it’s there for someone in finance or leadership. Most licences bought through the New Commerce Experience on annual terms can only be reduced at renewal, so put a note in the diary for whenever yours comes round.
If you’d like a second pair of eyes on which licences are still earning their keep, we’re happy to go through your tenant with you.
What a bigger mailbox means on a Mac
Outlook for Mac and Apple Mail both keep a local copy of mail so people can work offline. A mailbox that grows towards 100 GB will eventually take up a similar amount of space on the Mac’s drive. On a 256 GB MacBook Air already holding a synced OneDrive and a few Adobe libraries, that gets tight faster than people expect.
So the extra headroom is welcome, but Dr Logic still recommends a sensible retention or archiving policy for your heaviest users. Bigger mailboxes also take longer to migrate and restore, which is worth knowing before your next device refresh, and it’s one reason we back up Microsoft 365 mailboxes with CloudAlly for clients.
How to check a user’s quota
- Open the Microsoft 365 admin centre. Go to Users, then Active users.
- Select the user. Open the Licenses and apps tab.
- Expand the Business licence. Make sure both Exchange service plans are on.
- To see the effective limit, open Exchange Online PowerShell. Run Get-Mailbox -Identity ku.oc.niamodruoy@eman | Format-List ProhibitSendReceiveQuota. The result should show 100 GB.
If both plans are on and the quota still shows 50 GB, look for a custom quota on that mailbox before you change any licences.
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FAQs
Do I need to do anything to get the 100 GB mailbox?
No. Microsoft adds the extra storage automatically to Business Basic, Business Standard and Business Premium licences, and the rollout was due to finish by the end of September 2026. If a user still shows 50 GB, check that both Exchange service plans are switched on and that nobody has set a custom quota on the mailbox.
If a user has Business Premium and E3, do they get 200 GB?
No, they get 100 GB. Exchange doesn’t add mailbox quotas together across licences. It takes the highest entitlement from any one licence the user holds, and both Business Premium and Office 365 E3 now give 100 GB, so the limit stays at 100 GB whichever way you combine them.
Does the increase add archive space?
No. The extra 50 GB goes on the primary mailbox only. Archive capacity and compliance features stay as they were for each plan, so if you rely on archiving for your heaviest users, the existing setup still applies. Business Premium keeps the archiving it already included before this change.
Can we remove Exchange Online Plan 2 now?
Possibly, if storage was the only reason you added it. Plan 2 also brings larger archives and features such as litigation hold, so check whether anyone depends on those first. Annual subscriptions bought through Microsoft’s New Commerce Experience can usually only be reduced at renewal, so plan the change for then.
