Fixing a “Your Mailbox is Full” error in Microsoft Outlook is as easy as getting rid of unwanted items from your mailbox. You have multiple tools to help you find old and large items as well as a few other ways to reduce the mailbox size. We’ll show you what you can do.

Note that Outlook.com’s free version offers 15GB of storage, and Microsoft 365 subscribers get 50GB of storage. If you exceed this storage, you get the above error.

Use Mailbox Cleanup

The easiest way to find and remove items from Outlook mailbox is by using the app’s built-in cleanup tool. This tool helps find and remove old emails, find emails larger than the specified size, and automatically archive old emails.

To use the Mailbox Cleanup tool, first launch Outlook. In the app’s top-left corner, click “File.”

From the left sidebar, select “Info.” On the right pane, click Tools > Mailbox Cleanup.

The Mailbox Cleanup tool is now open on your screen. Click the relevant option to reduce your mailbox size:

• Find Items Older/Larger Than: This option helps find mailbox items that are older or larger than the specified value. For example, you can use this option to find extremely old emails or emails with large attachments.
• AutoArchive: This option helps you automatically move old emails to the archive folder. This doesn’t delete your emails; it only moves your emails out of your main inbox.
• Empty: This option permanently deletes the items you’ve temporarily removed.
• Delete: This option removes the alternate versions of files from your mailbox.

Depending on the option you choose, you’ll get further prompts, offering you the flexibility to choose what you want to remove. When you’ve finished using the tool, click “Close” to close the tool window.

Save Attachments Outside of Outlook

Every email attachment counts towards your Outlook account storage. If you often receive large attachments, or you’ve already received many attachments, save those files outside of Outlook. This frees up your Outlook storage and still gives you access to your file attachments.

To do that, open Outlook and find an email with an attachment you want to save to your computer.

Next to the attachment in the email, click the down-arrow icon and choose “Save As.” If the email has multiple attachments and you want to save them all at once, click “Save All Attachments” instead.

On the Save Attachment window, choose the folder to save the files in, then click “Save.” Optionally, rename the attachment by entering a name in the “File Name” field.

After saving the attachment to your computer’s storage, delete the original attachment in the email to free up your mailbox storage. Do that by selecting the same down-arrow icon next to the attachment and click “Remove Attachment.” In the open prompt, select “Remove Attachment.”

Repeat the above steps until you’ve saved all your email attachments to your computer.

Find and Remove Large Emails Manually

In Outlook, you can create search folders that only display the emails meeting your criteria. With this feature, you can create a folder that only shows large emails. This allows you to quickly find and remove unwanted memory-hogging emails from your Outlook storage.

To use that feature, launch Outlook. In the left sidebar, click “Search Folders” and choose “New Search Folder.”

On the New Search Folder window, in the Organizing Mail section, click “Large Mail.” In the Customize Search Folder section, select “Choose.” Specify the email size and click “OK.”

Then, choose “OK” on the open window.

In Outlook’s left sidebar, you’ll see your newly created search folder. Click the folder to find all the emails matching your specified criteria. To remove an email displayed in this folder, right-click that email and select “Delete.”

To delete multiple emails at once, select all the emails to remove, right-click a selected email, and choose “Delete.”

And that’s all.

Get Outlook to Automatically Remove Deleted Items

When you delete an item in Outlook, the app moves that item to the Deleted Items folder instead of permanently deleting it. Your “deleted” file still occupies your mailbox storage, as it still hasn’t been fully removed.

Luckily, you can get Outlook to automatically and permanently remove items from the Deleted Items folder.

To do that, launch Outlook, right-click the “Deleted Items” folder, and select “Properties.”

Access the “AutoArchive” tab. Enable the “Archive This Folder Using These Settings” option. In the “Clean Out Items Older Than” menu, specify the time duration and the unit. For example, clean out items that are older than 30 days.

Enable the “Permanently Delete Old Items” option, and choose “Apply” followed by “OK.”

Outlook will now delete your mailbox items using the specified criteria.

Make Outlook Automatically Archive Old Emails

Outlook offers the option to automatically archive old emails and save those emails as a file on your computer. This helps reduce your mailbox storage usage.

To use that feature, launch Outlook, select “File,” and choose “Options.”

In the left sidebar, click “Advanced.” On the right pane, in the AutoArchive section, choose “AutoArchive Settings.”

On the open window, turn on “Run AutoArchive Every X Days.” Replace X with the number of days you want Outlook to archive old emails automatically.

In the During AutoArchive section, specify how the feature should archive items. Then, click “OK.”

And you’re all set.

The tips above will help you reduce your Outlook mailbox storage usage, fixing the error you’re currently encountering in the app. You can then start sending and receiving emails, and perform other tasks in the app without any problems. Happy emailing!