Outlook Mailbox Full? Why You Can’t Send Mail and How to Free Space, Even After Deleting Everything
Outlook says your mailbox is full, email has stopped, and the warning may stay after you delete everything you can find. Here is what it means, what is using the space, and what frees it fastest.
In short: Outlook mailbox full means you have reached a storage limit, and sending or receiving stops until you are back under it. Deleting is not enough: mail moves to Deleted Items and still counts until you empty that folder. Empty it first. Then check Settings > Account > Storage (Accounts in the new Outlook) or, in classic Outlook, File > Tools > Mailbox Cleanup, and delete the largest messages. A free personal account has two limits: 15 GB for mail and 5 GB of Microsoft cloud storage shared with OneDrive. If the message says Microsoft Unified Storage is full, the 5 GB is what you need to clear. The Archive button frees nothing; an online archive or a .pst file can.
What “Mailbox Full” Means and What Stops Working
Personal Outlook.com accounts have two limits, and going over either one stops your email:
- Mailbox full or Quota Exceeded: your mail storage is over its limit. You can’t send or receive.
- Microsoft Unified Storage is full: your cloud storage is over its limit. You can’t send or receive even if the mailbox itself has room. OneDrive files also become read-only.
Email sent to you during this time does not wait for you. It goes back to the sender, who has to send it again. Stay over the cloud limit and Microsoft says your OneDrive is frozen after three months and may be deleted after six.
Microsoft 365 work and school mailboxes stop in three steps:
- Warning: an email says the mailbox is nearly full. Everything still works.
- Prohibit Send: you can’t send new messages. If you cannot send mail but mail still arrives, you are here.
- Prohibit Send/Receive: incoming mail is rejected, and the sender gets a delivery failure notice. You may see Quota Exceeded, your account is above quota limits.
How to See How Much Space You Use in Each Outlook
- New Outlook for Windows: Settings > Accounts > Storage shows the space each folder uses.
- Outlook on the web and Outlook.com: Settings > Account > Storage.
- Classic Outlook for Windows: File > Tools > Mailbox Cleanup, then View Mailbox Size.
- Outlook for Mac: Microsoft’s storage pages don’t cover the Mac app. Open Outlook on the web in a browser and use the route above.
- Microsoft cloud storage (personal accounts): this is a separate figure. Sign in to your account dashboard and open the Microsoft storage section.
Why Outlook Says Mailbox Full After Deleting Everything
- The mail is still in Deleted Items. Deleting moves mail there, and it keeps counting until the folder is emptied. Mail deleted with Sweep or Clean Up goes to the same place.
- The full limit is the other one. On a personal account, deleting mail frees cloud storage only where the mail had attachments. Clear OneDrive as well, then empty its Recycle bin online. Emptying your computer’s Recycle bin does not do this.
- The mail only moved. Mail in the Archive folder, or any other folder, is still in the mailbox.
- The figure has not caught up. Microsoft says the cloud storage figure can take up to 24 hours to update after you delete files. It gives no time for the mailbox figure. If nothing changes, check the Storage page on the web, not only in your desktop app.
- Recoverable Items is full (work accounts). Emptied mail goes to a hidden folder for a while, so it can be recovered. Microsoft says that folder has its own limit: 30 GB, or 100 GB on hold. When it fills, you can’t delete anything, and you may see The operation could not be completed. A separate article says the size you see leaves this folder out. If emptying Deleted Items doesn’t clear the warning on a work account, ask your IT admin to check this folder. Microsoft’s Outlook.com pages don’t say whether it counts on personal accounts.
The Fastest Ways to Free Space, Biggest Effect First
Start with Deleted Items, because it is one step. After that, let your folder sizes decide.
1. Empty Deleted Items. Do the same for Junk Email. It clears by itself within 30 days (one Microsoft page says as soon as 10), so don’t wait.
- New Outlook: right-click Deleted Items, then Empty.
- Classic Outlook: right-click Deleted Items, then Empty Folder.
- Web and Outlook.com: right-click Deleted Items, then Empty.
Emptied by mistake? Select Deleted Items and use Recover (Recover Deleted Items From Server in classic Outlook). Microsoft gives 30 days on Outlook.com and the web; its Exchange page gives 14 by default on work mailboxes.
2. Clear whole folders by age. In the new Outlook and on the web, the Storage page can permanently delete everything in a folder, or only items older than 3, 6 or 12 months. Look at Sent Items as well. In classic Outlook, use Find items older than in Mailbox Cleanup.
3. Find large attachments. To remove an attachment you have to delete its email.
- New Outlook and web: select Filter > Sort by > Size at the top of the message list. Select it again if the smallest come first. If your Outlook has a separate sort control, use that.
- Classic Outlook: Find items larger than in Mailbox Cleanup, or type messagesize:>5 MB in the Search box.
- To keep a file: open the email, select Save to OneDrive beneath the attachment, then delete the email with Shift + Delete. If your cloud storage is the full one, save it to a folder on your computer instead.
4. Use Sweep on the biggest senders. In the new Outlook and on the web, select an email and choose Sweep. You can delete everything from that sender (and, if you choose, everything they send later), keep only their latest message, or delete their mail older than 10 days. Empty Deleted Items afterwards, or the space stays used.
5. Use Clean Up in classic Outlook. Select a conversation, then Home > Clean Up > Clean Up Conversation. This removes only messages that repeat a later reply, so it may not free much. Archive, Sweep and Clean Up explains the differences.
Still full? A paid subscription raises a personal mailbox to 100 GB, the most a consumer account can have; trials don’t qualify. At work, ask your IT admin, who may have set your limit below your plan’s.
Outlook Mailbox Limits by Account Type
| Account | Mailbox | Warning / no send / no send or receive | Archive mailbox |
|---|---|---|---|
| Outlook.com, no subscription | 15 GB, plus 5 GB of cloud storage | Both stop at either limit | Not covered by Microsoft’s pages |
| Outlook.com, Microsoft 365 subscription | 100 GB, plus your plan’s cloud storage | Both stop at either limit | Not covered by Microsoft’s pages |
| Business Basic, Business Standard | 100 GB | 98 / 99 / 100 GB | 50 GB |
| Business Premium, E3, E5, Exchange Online Plan 2 | 100 GB | 98 / 99 / 100 GB | 100 GB, up to 1.5 TB with auto-expanding archiving |
| Office 365 E1, Exchange Online Plan 1 | 50 GB | 49 / 49.5 / 50 GB | 50 GB |
| F3, Exchange Online Kiosk | 2 GB | 1.96 / 1.98 / 2 GB | Not included |
The work figures are the maximums in Exchange Online limits. Admins can set them lower, and only an admin can turn on an archive mailbox.
Personal storage changed recently. Cloud storage is 100 GB on Basic and 1 TB on Personal. New Family and Premium subscriptions from October 8, 2026 get 2 TB shared across the family, and existing ones move to that at renewal from May 2, 2027. More cloud storage does not raise the 100 GB mailbox limit. If a subscription ends, you drop back to 15 GB and 5 GB, and being over those stops your email.
Outlook Mailbox Full: How to Archive So It Frees Space
- The Archive button does not free space. It moves mail to the Archive folder in the same mailbox, and Microsoft says your mailbox size stays the same.
- An online archive does, if you have one. It is a second mailbox for older mail, turned on by an admin. Look for Online Archive (classic Outlook, Mac) or In-Place Archive (new Outlook, web) in your folder list. Move or drag mail into it. In classic Outlook, searches from your Inbox don’t include it. Microsoft describes it only for work and school mailboxes.
- A .pst file does. It is a separate file on your computer. In classic Outlook, go to File > Info > Tools > Clean up old items, choose Archive this folder and all subfolders, pick the folder, enter a date under Archive items older than, and select OK. The command may be missing at work if an admin has turned it off.
- The new Outlook can use a .pst too, with conditions. Open one under Settings > Files > Outlook Data Files and drag mail into it. It needs classic Outlook installed too and a Microsoft 365 subscription.
Exporting to a .pst is described as a backup, so the mail stays in your mailbox until you delete it. A .pst sits on one computer, so back it up, but keep it out of a synced OneDrive folder: Microsoft warns that a large one can slow OneDrive sync.
Moving old emails automatically covers what each Outlook can do by itself. If mail seems to have gone missing during a clean-up, see where disappearing Outlook emails usually go.
Frequently Asked Questions
Why is my Outlook mailbox still full after deleting everything?
Deleted mail goes to Deleted Items and counts until that folder is emptied. On a personal account the full limit may also be your 5 GB of Microsoft cloud storage, which OneDrive files use too.
Why can’t I send mail when my Outlook mailbox is full?
Over its limit, a personal Outlook.com account can’t send or receive. A Microsoft 365 work mailbox stops sending first, then stops receiving when it reaches its full limit.
Does the Archive button free up space in Outlook?
No. It moves mail to the Archive folder in the same mailbox, so Microsoft says your mailbox size stays the same. An online archive mailbox or a .pst file takes mail out of your main mailbox.
Does OneDrive count toward my Outlook storage?
On a personal account, partly. Your mail has its own allowance, 15 GB on a free account. OneDrive shares a separate 5 GB of cloud storage with Outlook.com attachments, and being over either limit stops your email. Attachments count toward both.
How do I check my mailbox size in Outlook?
New Outlook: Settings > Accounts > Storage. Outlook on the web and Outlook.com: Settings > Account > Storage. Classic Outlook: File > Tools > Mailbox Cleanup > View Mailbox Size.