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Outlook "Your mailbox is full": what it means and how to fix it

Short answer

"Your mailbox is full" means your email account has used up its storage limit, so Outlook may stop sending and receiving mail. The quickest fix is to delete large emails with attachments, then empty Deleted Items and Junk Email. Deleted mail keeps counting against your limit until you empty those folders. On Outlook.com, attachments also use your 5 GB Microsoft cloud storage.

What this message means

The message comes from your mail server, not from your computer. Every mailbox has a storage limit: 15 GB for a free Outlook.com mailbox, 100 GB with a Microsoft 365 Personal or Family subscription, and usually 50 GB or 100 GB for work or school accounts (your IT admin may set a lower limit). Close to the limit you get warnings. Once you go over it, you can't send email, and eventually new email is rejected too. People who write to you get a bounce message saying your mailbox is full. Everything counts toward the limit, including Deleted Items, Junk Email, Sent Items and attachments. Deleting files on your computer does not help.

Common causes

CauseHow to tell
Deleted Items and Junk Email were never emptiedIn Settings > Accounts > Storage (new Outlook and Outlook on the web), Deleted Items or Junk Email shows several GB. Deleting mail from the Inbox made no difference to the used figure.
Old emails with large attachments or photosWhen you sort any folder by size, the top messages are several MB each. Inbox and Sent Items are the largest folders in the storage breakdown.
Outlook.com only: your 5 GB Microsoft cloud storage is full, even though the mailbox isn'tYour email use is well under 15 GB, but the Microsoft account storage page shows cloud storage (OneDrive files plus Outlook attachments) at or above 5 GB. The warning may say "Your cloud storage is full" and OneDrive files become read-only.
Work or school mailbox has hit a limit set by your administratorYou sign in with a company or school address. The limit shown in Storage is lower than you expected (for example 2 GB or 50 GB), and you received "Quota Exceeded" or "Prohibit Send" notification emails.
Mail was moved to the Archive folder, which stays in the same mailboxYou clicked Archive on lots of mail but the used storage didn't drop. The regular Archive folder counts toward your limit. Only a separate Online Archive (In-Place Archive) mailbox frees space.
A non-Microsoft account (Gmail, ISP or IMAP/POP) added to Outlook is full at the providerThe warning appears only for that account. The provider's own webmail or storage page shows it at its limit.

How to fix it

1. Check what is using the space

New Outlook for Windows and Outlook on the web / Outlook.com. Classic Outlook for Windows: File > Info > Tools > Mailbox Cleanup > View Mailbox Size.

  1. In new Outlook, select Settings (gear icon) > Accounts > Storage. In Outlook on the web, select Settings > Account > Storage.
  2. Note the used amount and the per-folder breakdown.
  3. If a folder is large, use its option to permanently delete all items, or only items older than 3, 6 or 12 months.
  4. On Outlook.com, also check your Microsoft account storage page. If cloud storage is at 5 GB, see the OneDrive fix below.

2. Empty Deleted Items and Junk Email

  1. Right-click the Deleted Items folder and choose Empty folder (in classic Outlook for Windows and Outlook for Mac, choose Empty Folder or Empty).
  2. Confirm the permanent deletion.
  3. Do the same for Junk Email.
  4. From now on, press Shift+Delete to delete a message permanently so it never lands in Deleted Items (Windows and web).
  5. Wait a few minutes, then check the storage figure again. The server can take a while to update.

3. Find and remove large emails and attachments

Steps are for Outlook on the web / new Outlook. In classic Outlook for Windows, use File > Info > Tools > Mailbox Cleanup > Find items larger than.

  1. Open Inbox (and later Sent Items). At the top of the message list, select Filter > Sort by > Size.
  2. If the smallest messages show first, select Filter > Sort by > Size again so the largest are on top.
  3. Open a large message and, under the attachment, select Save to OneDrive or download it to your computer.
  4. Select the message and press Shift+Delete to remove it permanently.
  5. Repeat until you are comfortably below the limit (aim for at least 10% free).

4. Outlook.com: free up Microsoft cloud storage

Personal Outlook.com, Hotmail and Live accounts only

  1. Sign in to your Microsoft account and open the storage page to see how the 5 GB free cloud storage is split between OneDrive and Outlook attachments.
  2. Delete large files you no longer need from OneDrive, then empty the OneDrive Recycle bin.
  3. Delete emails with large attachments in Outlook.com, then empty Deleted Items.
  4. If you still need more room, a Microsoft 365 Personal or Family subscription raises cloud storage to 1 TB and the mailbox limit to 100 GB.

5. Work or school account: purge Recoverable Items and use the Online Archive

Microsoft 365 / Exchange Online work or school accounts

  1. In Outlook on the web, open Deleted Items and select Recover items deleted from this folder. In classic Outlook, go to Folder > Recover Deleted Items.
  2. Select the items you don't need and delete them permanently (this doesn't work for mailboxes on legal hold).
  3. If you see an In-Place Archive or Online Archive folder, drag older folders or messages into it. That archive is a separate mailbox and frees space.
  4. Don't rely on the ordinary Archive folder, which counts toward the same limit.

6. Ask your IT admin for more space

Work or school accounts

  1. Send your admin the exact warning and the used/limit figure from Settings > Accounts > Storage.
  2. Ask them to raise your mailbox quota (Exchange Online allows up to 100 GB on most business and enterprise plans, 50 GB on Office 365 E1) or enable an Online Archive.
  3. Once the change is made, restart Outlook so the new limit shows.

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Still not fixed?

If the warning stays after you've cleaned up, sign in to Outlook on the web and check Storage there. Classic Outlook's cached view can lag behind the server, and the server can take up to a few hours to recalculate. If you're below the limit on the web but the desktop app still complains, restart Outlook or remove and re-add the account. For a personal Outlook.com account, contact Microsoft Support from the Help (?) menu in Outlook.com. For a work or school account, only your IT administrator can change quotas, enable the Online Archive or clear items kept on hold. If the account belongs to another provider (Gmail, an ISP), free up space in that provider's webmail.

Questions people ask

Why is my Outlook mailbox still full after I deleted emails?

Deleted messages go to Deleted Items and still count toward your limit until you empty that folder. On work accounts they then sit in Recoverable Items for a while. Empty Deleted Items and Junk Email, then allow a few minutes (sometimes hours) for the storage figure to update.

I have 1 TB of OneDrive storage, so why is my mailbox full?

Mailbox storage and OneDrive storage are separate. A Microsoft 365 subscription gives an Outlook.com mailbox up to 100 GB, and work mailboxes usually get 50 GB or 100 GB, regardless of how much OneDrive space you have.

Will I lose my emails if my mailbox is full?

No, existing mail stays. You won't be able to send, and new incoming mail may be rejected and bounced back to the sender until you get under the limit. Those rejected messages aren't delivered later, so senders have to resend.

Is a "Your mailbox is full" email a scam?

Often, yes. Phishing emails copy this warning to steal passwords. Don't click links in the email. Check your storage yourself in Outlook under Settings > Accounts > Storage, or by signing in to your account directly.

Does archiving emails free up space in Outlook?

Only if they go somewhere outside your mailbox. The regular Archive folder counts toward your limit. An Online Archive (work accounts) or a .pst file on your computer (classic Outlook for Windows) does free space.

Sources

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