Fix Outlook Mailbox Full Cannot Receive Mail

If your Outlook mailbox is full and you cannot receive mail, the fix is to free up storage space by deleting or archiving old items, then reduce the mailbox size going forward. This article explains why the problem happens, how to clear space quickly, and how to prevent it from recurring.

Why Outlook Stops Receiving Mail When Full

Outlook stores your email, calendar, contacts, and tasks in a data file. When that file reaches the size limit set by your email provider or by the Outlook application itself, the server rejects new incoming messages. The sender may receive a bounce-back message saying your mailbox is full, or the message simply stays on the server until space is freed.

The most common limits are:

Microsoft 365 / Exchange Online: 50 GB mailbox limit (100 GB for some plans).
Outlook.com: 15 GB free storage.
POP/IMAP accounts: Limits are set by your email provider (often 1–10 GB).
Outlook data file (.pst): Older versions had a 2 GB limit; newer versions allow up to 50 GB, but performance degrades as it grows.

The warning “Your mailbox is full” usually appears when you are near the limit, but you may not see it until you try to send or receive. Once the limit is hit, you can still read and search existing mail, but new mail is blocked.

Quick Fix: Free Up Space in Outlook

Start with these steps to make room immediately. The goal is to reduce the total size of your mailbox so the server accepts new messages.

Empty the Deleted Items folder. Right-click the folder and choose “Empty Folder.” This is often the largest source of recoverable space.
Delete large attachments. Use the search box to find messages with attachments, or sort by size if your view supports it. Delete or save attachments to your computer and remove them from the message.
Clear the Junk Email folder. Permanently delete items there.
Archive old mail. Move items older than a year to an archive folder or export them to a .pst file.
Compact the data file. In Outlook, go to File > Account Settings > Data Files, select the file, and click “Settings” > “Compact Now.” This reduces the physical file size after deletions.

After freeing space, restart Outlook and try sending a test message to yourself. If it arrives, the issue is resolved.

How to Check Your Current Mailbox Size

You need to know how much space you are using to decide how much to delete. The method depends on your account type.

Microsoft 365 / Exchange: In Outlook, go to File > Account Settings > Account Settings, select your Exchange account, and click “Change.” Look for “Mailbox Cleanup” or “View mailbox size.” You can also check online in Outlook on the web under Settings > View all Outlook settings > General > Storage.
Outlook.com: Sign in to the web app, click the gear icon, then “View all Outlook settings” > “General” > “Storage.” It shows a bar chart of used space.
POP/IMAP: The size is not shown in Outlook. Check your provider’s webmail interface or account dashboard.

If you cannot find the size, a rough estimate is to look at the size of your .ost or .pst file on disk. In Outlook, right-click the data file in Account Settings and choose “Open File Location.” The file size is a good proxy for mailbox size.

Prevent the Problem from Returning

Once you have cleared space, adopt habits that keep your mailbox under the limit. The most effective strategies are:

Enable auto-archive. Outlook can automatically move items older than a set number of days to an archive file. Go to File > Options > Advanced > AutoArchive Settings.
Use retention policies. If your organization provides them, they can delete or archive old items automatically.
Reduce attachment size. Send links to cloud storage instead of attaching large files.
Unsubscribe from newsletters. Delete them regularly instead of letting them accumulate.
Empty Deleted Items on exit. In Outlook, go to File > Options > Advanced and check “Empty Deleted Items folder when exiting Outlook.”

If you consistently stay near the limit, consider upgrading your plan or moving to a provider with a larger quota.

What to Do If You Still Can’t Receive Mail

If you have freed space and the problem persists, the issue may be elsewhere. Check these in order:

Verify the server-side limit. Even if your local file is small, the server may have a separate quota. Log into webmail to see the actual server usage.
Check for a sending limit. Some providers block receiving if you have exceeded a daily send limit, not just storage. Wait 24 hours or contact support.
Look for a forwarding rule. A rule that forwards all mail to another address can cause messages to disappear. Check Rules in Outlook and webmail.
Test with another client. Send a test to your address and see if it appears in webmail. If it does, the problem is local to Outlook.
Repair the data file. Close Outlook, then run the Inbox Repair tool (scanpst.exe) on your .pst file. For .ost files, you can delete the file and let Outlook recreate it (this will resync from the server).

If none of these work, contact your email provider’s support. They can check if the server is rejecting messages due to a full mailbox or another issue.

Common Misconceptions About Mailbox Limits

Many users believe that deleting messages from the Inbox is enough. That is not always true. The mailbox size includes all folders: Sent Items, Drafts, Deleted Items, and even Junk. Also, items in the “Recoverable Items” folder (like those in the Deleted Items after you empty it) still count toward the limit until they are purged by retention policies. In Exchange Online, recoverable items can be up to 30 GB and are not visible in normal views. To permanently purge them, you may need to use the “Purge” option in Outlook Web App or wait for the retention period to pass.

Another misconception is that compressing the data file reduces the mailbox size on the server. It only reduces the local file size. To reduce server usage, you must delete items permanently from the server, which happens when you empty Deleted Items and purge recoverable items.

Frequently Asked Questions

How do I know if my mailbox is full?

Outlook will show a warning message when you are near the limit, but the most reliable way is to check your mailbox size in the web interface or in Outlook’s account settings. If you cannot send or receive, and the sender gets a “mailbox full” bounce, that confirms it.

Can I increase my Outlook mailbox size?

For Microsoft 365, you can buy extra storage (up to 100 GB) or enable auto-expanding archiving. For Outlook.com, you can purchase additional storage. For other providers, you may need to upgrade your plan or ask your administrator.

Will deleting emails from my phone free up space?

If your phone is configured as IMAP, deleting on the phone deletes from the server, so yes. If it is POP, deletions may only affect the phone. Check your account settings to be sure.

What is the difference between archiving and deleting?

Deleting removes the item permanently. Archiving moves it to a separate data file (usually a .pst) that is not counted in your mailbox quota. You can still search and access archived items, but they do not take up server space.

Why does my mailbox say full when I have only a few emails?

Large attachments, hidden recoverable items, or a small quota (like 1 GB) can fill up quickly. Check the size of your Sent Items and Deleted Items, and look for messages with large attachments.

Can I use Outlook with a full mailbox?

You can read and search existing mail, but you cannot send or receive new messages. Some features like calendar sharing may also stop working. Free up space as soon as possible.

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

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