How to See Your Outlook Mailbox Size and the Exchange Online Limit

If Outlook warns that your mailbox is almost full, you need two numbers: how much you use and what your limit is. Both are easy to check, but the place to look is different in classic Outlook, new Outlook, Outlook on the web and Mac. In this guide, I’ll show how to see Outlook mailbox size in each client, the current Exchange Online limits per plan, and why the numbers sometimes do not match.

Quick Answer: Classic Outlook for Windows shows it under File > Tools > Mailbox Cleanup > View Mailbox Size. New Outlook for Windows has it in Settings > Accounts > Storage, and Outlook on the web in Settings > Account > Storage. Most Microsoft 365 business and enterprise plans now give a 100 GB primary mailbox, but your IT team can set a lower quota.

Exchange Online Mailbox Size Limits by Plan

Your limit depends on the Microsoft 365 license, not on the Outlook version. If you connect a Gmail, Yahoo or other IMAP account to Outlook, the limit comes from that provider instead.

Here are the current Exchange Online numbers from Microsoft’s Exchange Online limits page:

Plan	Primary mailbox	Archive mailbox
Microsoft 365 Business Basic, Business Standard	100 GB	50 GB
Microsoft 365 Business Premium, E3, E5, Office 365 E3/E5, Exchange Online Plan 2	100 GB	Starts at 100 GB, auto-expands up to 1.5 TB
Office 365 E1, Exchange Online Plan 1	50 GB	50 GB
Microsoft 365 F3, Exchange Online Kiosk	2 GB	None (needs the Exchange Online Archiving add-on)

A few points that are not obvious from the table:

• Business Basic and Business Standard were 50 GB until recently. Microsoft announced the move to 100 GB in message center post MC1304290 (May 2026), with the rollout planned to finish by 30 September 2026. It covers the primary mailbox only. The archive on these two plans stays at 50 GB.
• If an admin set a custom quota on a mailbox earlier, that quota stays. So some mailboxes still show 50 GB after the rollout until IT changes it.
• Quotas do not add up. A user with Business Standard plus an Exchange Online Plan 2 license still gets 100 GB, even if an admin portal shows 150 GB.
• Shared mailboxes get 50 GB without a license. For 100 GB or an archive, the shared mailbox needs Exchange Online Plan 2 (or Plan 1 plus Exchange Online Archiving).
• Microsoft has also announced 3 TB auto-expanding archives (MC1472592), rolling out from mid to late October 2026. It is limited to E5 and the Purview compliance licenses. E3, Business Premium and Plan 2 stay at 1.5 TB.

On a 100 GB mailbox, the warning comes at 98 GB. Sending stops at 99 GB, and at 100 GB the mailbox stops receiving too. A 50 GB mailbox uses 49, 49.5 and 50 GB.

In our environment, every user with the right license started showing 100 GB after the rollout. If one of your users still shows 50 GB, look for an old custom quota on that mailbox first (the Set-Mailbox command further down fixes it).

How to See Outlook Mailbox Size in Classic Outlook for Windows

Classic Outlook (Outlook 2016/2019/2021/2024 and Microsoft 365 Apps) gives you three places to check.

1) The Usage Bar on File > Info

1. Click File.
2. On the Info page, look under Mailbox Settings. The bar shows how much space is free out of your total, for example “45 GB free of 99 GB”.

This is the fastest check, and for Exchange accounts it shows the mailbox on the server.

2) Mailbox Cleanup > View Mailbox Size

This gives the size of every folder in one window.

1. Click File, then Tools (next to Mailbox Settings), then Mailbox Cleanup.
2. Click View Mailbox Size.
3. The Folder Size window lists the total and each folder with its subfolders.

3) Folder Size From Data File Properties

1. Right-click your email address (the top of the mailbox) in the folder pane and select Data File Properties.
2. Click Folder Size.
3. Use the Local Data and Server Data tabs to compare the copy on your PC with the copy in Exchange Online.

The two tabs often show different numbers. That is normal (explained further down).

You can also right-click the status bar at the bottom of Outlook and tick Quota Information. The used space then stays visible at all times, which is handy for users who are close to the limit.

How to See Mailbox Size in New Outlook for Windows

New Outlook has no File menu, so the steps above do not apply.

1. Click the Settings gear at the top right.
2. Go to Accounts > Storage.
3. You see the total used and a breakdown by folder.

From the same page you can empty a folder or delete items older than 3, 6 or 12 months. Use that carefully on Inbox and Sent Items, because the deleted items go to Deleted Items first and still count until that folder is emptied.

If you are not sure which Outlook you are on, here is how to check your Outlook version.

How to See Mailbox Size in Outlook on the Web

1. Sign in to Outlook on the web and click the Settings gear.
2. Open Account > Storage.

Older guides still say Settings > General > Storage. That path has moved. The Storage page here works the same way as in new Outlook, with the same cleanup options.

When a user tells me Outlook is full, I check classic Outlook first. Since I have Microsoft 365 admin access, I also open their mailbox in the Exchange admin center to see the real size on the server. Outlook only shows part of the picture.

Outlook for Mac and Mobile

In legacy Outlook for Mac, right-click the account in the sidebar, select Properties, then open the Storage tab. New Outlook for Mac has no storage view at the moment, so use Outlook on the web.

Outlook for iOS and Android do not show mailbox size at all. Check it from a computer or a browser.

Why Outlook Says the Mailbox Is Full When It Shows Free Space

There are three usual reasons.

The Recoverable Items folder is full. When you empty Deleted Items, the mail goes to a hidden folder called Recoverable Items. It has its own quota: 30 GB normally, 100 GB when the mailbox is on hold or under a retention policy (105 GB with an archive).

Outlook does not show this folder in any of the size views above. So the user sees free space while Exchange blocks new mail. Only an admin can see it and clean it (PowerShell section below).

If you deleted something by mistake and it is still in Deleted Items, you can move deleted items back to the Inbox.

The OST file is not the mailbox. Classic Outlook keeps a local copy in an OST file. By default it only syncs part of your mail, based on your disk size. So Local Data in Folder Size can be much smaller than Server Data. The setting is Download email for the past under File > Account Settings > Account Settings, then double-click the Exchange account. The OST itself has a separate default maximum of 50 GB. It is a limit on the file on your PC, not on your mailbox.

The quota is lower than you think. IT can set any quota below the plan limit. The File > Info bar shows your real quota, not the plan’s.

Check Mailbox Size as an Admin

If you support users, the Outlook views above are not enough because they hide Recoverable Items and the archive.

Microsoft 365 admin center: go to Reports > Usage, pick Exchange, then the Mailbox usage report. It shows storage used, deleted item size and the quotas for every mailbox. The data is 24 to 48 hours behind.

Exchange admin center: go to Recipients > Mailboxes, select the mailbox, and on the General tab look at Mailbox usage.

PowerShell: install the ExchangeOnlineManagement module (Exchange Online PowerShell V3) and connect with an account that has Exchange admin rights.

Connect-ExchangeOnline
Get-EXOMailboxStatistics -Identity user@domain.com | Format-List DisplayName,TotalItemSize,TotalDeletedItemSize,StorageLimitStatus

TotalItemSize is what the user sees in Outlook. TotalDeletedItemSize is the Recoverable Items folder. If the second one is close to 30 GB, you found the problem.

For the archive, add -Archive:

Get-EXOMailboxStatistics -Identity user@domain.com -Archive | Format-List TotalItemSize

To see the quotas set on the mailbox:

Get-Mailbox user@domain.com | Format-List IssueWarningQuota,ProhibitSendQuota,ProhibitSendReceiveQuota,RecoverableItemsQuota

To raise a mailbox that is stuck on an old custom quota to the 100 GB plan values, use Set-Mailbox:

Set-Mailbox user@domain.com -IssueWarningQuota 98GB -ProhibitSendQuota 99GB -ProhibitSendReceiveQuota 100GB -UseDatabaseQuotaDefaults $false

For shared mailboxes, the same commands work. You can also see who has access to a shared mailbox before you start cleaning it.

Free Up Space Before You Hit the Limit

Start with these, in this order:

1. Find the big items first. Sort Inbox and Sent Items by size, then delete them or save the attachments to OneDrive or SharePoint.
2. Empty Deleted Items and Junk Email. Until you do, the mail still counts.
3. Turn on the online archive if your plan has one, and let the retention policy move old mail there. The archive has its own quota and does not count against the 100 GB.
4. Do not move mail to a PST file at work unless IT allows it. PST files sit on one PC and are not backed up with the mailbox. If you do use one, here is where the Outlook PST file is stored.

Microsoft’s own mailbox storage limits in Outlook page has the cleanup steps for each client if you want the official version.

If the File > Info bar shows free space but Outlook still refuses to send, do not keep deleting mail. Ask IT to check TotalDeletedItemSize first. That one number usually explains it.