Microsoft 365 guide

Business Basic Storage Limits: Mailbox, Archive and OneDrive

By Gander Web · Checked against Microsoft's documentation on 9 October 2026 · 6 min read

The limits at a glance

Your mailbox: 100 GB

Microsoft's Exchange Online limits now list user mailboxes on Business Basic, Standard and Premium at 100 GB. The extra space arrived during 2026 as a second 50 GB storage plan inside the same licence, rolled out tenant by tenant. If a mailbox still shows 50 GB, check two things: that the user's licence has all its service plans switched on, and that nobody set a custom mailbox quota before the change, because Microsoft left custom quotas alone.

To check how full a mailbox is, the user can open Outlook on the web and look under Settings > Account > Storage (Accounts in the new Outlook), which also breaks usage down by folder. As an admin, PowerShell gives you exact numbers:

Connect-ExchangeOnline
Get-MailboxStatistics [email protected] | Format-List TotalItemSize
Get-Mailbox [email protected] | Format-List ProhibitSendQuota,ProhibitSendReceiveQuota

When it fills up, Outlook warns first, then sending stops, and at the full limit incoming mail bounces back to the sender. The usual cause is years of attachments, so the archive below is the first fix.

The archive: 50 GB, switched off by default

Business Basic includes an archive mailbox of 50 GB per person. It's a separate store that shows up as In-Place Archive in Outlook on the web, and it doesn't count towards the 100 GB.

1. Open the Exchange admin centre and go to Recipients > Mailboxes.
2. Select the person, open the Others tab and choose Manage mailbox archive.
3. Turn the archive on and save.

Microsoft's default retention policy then moves items older than two years into the archive automatically. Microsoft notes the policy only runs on mailboxes bigger than 10 MB, so a brand-new mailbox won't move anything yet.

On Basic the archive stops at 50 GB. Auto-expanding archives up to 1.5 TB need the Exchange Online Archiving add-on or Business Premium.

OneDrive: 1 TB each

Every user gets 1 TB of OneDrive. OneDrive on the web shows how much you've used in the left-hand menu, and admins can see everyone's usage under Reports > Usage in the admin centre.

On the Business plans, 1 TB per person is the ceiling. If someone is outgrowing it, the files are usually shared material (photos, drawings, old projects) that belongs in a SharePoint or Teams site, which draws on the company pool instead.

SharePoint and Teams: one shared pool

SharePoint storage is shared across the business: 1 TB plus 10 GB for every licence. Ten Business Basic users get 1 TB plus 100 GB. Every Teams channel's files live in SharePoint, so they count towards the same pool, and so does every saved version of every file.

Check usage in the SharePoint admin centre, under Sites > Active sites. If you run out, Microsoft sells Office 365 Extra File Storage by the gigabyte. It adds to the SharePoint pool, not to anyone's OneDrive.

What happens to a leaver's storage

This is where businesses lose files without realising. When you remove someone's licence, their mailbox and OneDrive follow different clocks:

Getting files back from an archived OneDrive means either giving the person a licence again or enabling Microsoft's pay-as-you-go billing, which Microsoft prices at $0.60 per GB to reactivate plus $0.05 per GB per month for every archived account. For a leaver with a few hundred GB that adds up quickly.

Do it in this order instead:

1. Convert their mailbox to a shared mailbox while it's still licensed (it must be under 50 GB to drop the licence). Here's how.
2. Move their OneDrive files to a SharePoint site or a colleague's OneDrive while they're still licensed. Their SharePoint and Teams files stay where they are.
3. Then remove the licence. Don't delete the account if you converted the mailbox: Microsoft notes the shared mailbox still needs it.

If you'd rather delete the person outright, the admin centre's delete flow offers to give someone else access to their email (which converts it to a shared mailbox) and to their OneDrive. By default you then have 30 days to move the OneDrive files before it goes to the recycle bin.

Big attachments and bulk email

The default limit is 35 MB per message, and the Outlook phone app tops out at 33 MB even if an admin raises the limit. For anything large, share a OneDrive link instead: it doesn't fill the recipient's mailbox and you can stop sharing later.

Exchange Online allows 10,000 recipients a day per mailbox, and Microsoft also caps how many external recipients the whole business can email per day, based on your number of licences. Microsoft is clear that it isn't built for newsletters or marketing, so use a mailing service for those.

Questions

Related guides

Sources

1. Exchange Online limits
2. Manage unlicensed OneDrive user accounts
3. Plan for SharePoint storage
4. Office 365 IT Pros: 100 GB mailbox quotas for Microsoft 365 Business tenants
5. Create a shared mailbox (Microsoft 365 admin)

We checked every limit, menu path and date in this guide against the sources above on 9 October 2026. Microsoft changes these often. If something here no longer matches what you see, tell us and we'll update it.