Key Takeaways
- Your Outlook mailbox has a 15 GB storage limit for free accounts and 100 GB for Microsoft 365 subscribers (depending on your plan).
- Deleted Items and Junk Email folders both count toward your quota until permanently emptied.
- A full OneDrive account blocks Outlook from sending and receiving email even if your mailbox still has space.
- After clearing storage or upgrading, mail flow can take 24-48 hours to restore.
- Clean Email’s Auto Clean rules can prevent the Outlook mailbox from filling up again automatically.
Why Do I See the “Outlook Mailbox Full” Error?
Maybe you’re expecting an important message or need to send an email immediately and see a message that your Outlook is full. What does this message mean and what can you do about it?
If you see a "Your mailbox is full, you may not be able to send or receive items" or similar message in Outlook, this means you’ve reached the storage limit for your mailbox.
Most free Outlook.com accounts include 15 GB of mailbox storage, and most Microsoft 365 consumer subscriptions support up to 100 GB of mailbox storage, depending on your plan. All folders, including Sent and Deleted Items, count toward the Outlook email storage limit.
Where to check storage
- Outlook on the Web (Outlook.com / new Outlook):
Go to Settings (gear icon) → Accounts → Storage. From here, you can see your current usage and select Clean up mailbox to quickly delete items older than 3, 6, or 12 months. Don’t forget to empty the Deleted Items folder – it still counts toward your limit.
- Outlook Desktop (Windows/Mac):
In the Outlook app, click File → Tools → Mailbox Cleanup. This panel lets you view the size of each folder, find and delete large items, and set up AutoArchive rules to prevent future overflow.
Best Ways to Fix Outlook Mailbox Full Storage
We’ll walk you through several basic and advanced Microsoft Outlook tips for returning storage space to your mailbox. For Outlook on your desktop, the web, and your account in Clean Email, you’ll be back in business with emails flowing in just minutes.
Fix full storage in Outlook on the desktop
💡 New Outlook vs. Classic Outlook: The File → Tools → Mailbox Cleanup path below applies to Classic Outlook desktop only. If you’re using New Outlook (no File menu is visible at the top), skip to the Outlook.com steps instead – the web interface works the same way.
If your preferred method for using Outlook is the desktop application, you can use the built-in Outlook mailbox cleanup tool.
- Open the desktop application and go to the File tab.
- Select Info and open the Tools menu to pick Mailbox Cleanup.
- You’ll see a handful of options to clean up your mailbox and regain some storage space. You can locate and delete old emails in Outlook, use the AutoArchive feature, empty your deleted items, and remove conflicts. Simply pick an option and follow the prompts.
- When you finish, you can choose View Mailbox Size at the top to see the updated amounts. Then, click Close when you’re done.
Consider using these steps to clean up your Outlook mailbox regularly to keep your used storage under control.
Fix full storage on Outlook.com
Maybe you prefer to head to the web to manage your inbox. Although you won’t find the same Outlook cleanup tool as on desktop, here’s how to check your Outlook storage and then get it under control.
- Visit https://outlook.live.com/mail and log in with your Microsoft account.
- Select the Settings gear icon on the top right.
- In the pop-up window, choose General on the far left and Storage to the right.
- On the far right, expand the Email storage option. You’ll see your total storage amount along with how much you’ve used.
- Beneath Manage storage, you can empty folders such as Junk Email, Deleted Items, Sent Items, and others. Conveniently, you’ll see how much storage the folder uses and the number of messages within it.
- Open the Empty drop-down menu to the right and pick All or choose an option like 3, 6, or 12 months and older.
- Select OK when the confirmation box appears and check out your updated mailbox size.
Remember, you can perform the above steps on a regular basis to better manage your storage and organize Outlook emails wisely.
Fix full storage in the Outlook Mobile app
On the Outlook mobile app, you can free up space almost as easily as on desktop or web. Start by adjusting your swipe settings. Go to Settings → Mail → Swipe Options, and set your Swipe Action to Delete for faster cleanup.
Make sure to check the Junk and Deleted folders as well. Even on mobile, messages stored there still count toward your limit until you remove them completely.
Attachments are another common cause of a full mailbox. Open any message with large files, save the attachments to your phone or cloud storage, and then remove the email entirely. If you want to pinpoint the biggest space hogs, use the search bar to look for emails with attachments or sort messages by size.
📱 Seeing this error on iPhone? If your iPhone Mail app shows “Cannot Send Mail – The mailbox is full,” the problem is your Microsoft account’s storage, not your iPhone storage. There is nothing to fix on the phone itself. Follow the Outlook.com steps above to free up space, and the error will clear once your account is back under its storage limit.
Fix Full Outlook Storage Faster with Clean Email
While the cleaning tools Microsoft provides for Outlook on the desktop and web may be sufficient for freeing up some space, you can take your cleanup a step further.
3 first action steps to clear Outlook storage with Clean Email app:
- Delete old emails that you no longer need.
- Find and remove large emails that take up the most space
- Find out who sends you the most emails and remove unimportant senders.
Important: After completing these actions, remember to clear the Trash folder, as all the emails you deleted stay there and still count toward your storage.
Troubleshooting: If You Still Cannot Send or Receive Emails
If your Outlook mailbox has reached its limit, you may experience issues such as being unable to send or receive emails. In some cases, senders will receive a mailbox full bounce message when trying to contact you. Use the following steps to resolve the problem depending on your account type and situation:
- Start by clearing the Deleted Items and Junk folders. They continue to count toward your storage until emptied.
- Next, check for large emails and attachments. Sort your mailbox by size or use the search term hasattachments:yes. Save any files you need, then delete the messages with Shift + Delete to free space immediately.
- 📌 On the desktop app, open the Mailbox Cleanup tool from File → Tools. It shows folder sizes, helps remove old items, and lets you enable AutoArchive so older mail moves out automatically.
- 📌 On the web, go to Settings → Accounts → Storage. The Clean up mailbox option can remove messages older than 3, 6, or 12 months with one click.
Why Outlook might be blocked even when your mailbox looks fine
If you’ve cleared your Outlook mailbox but still can’t send or receive email, the issue may not be your mailbox at all – it may be your OneDrive.
Outlook.com and OneDrive share the same Microsoft cloud storage pool for OneDrive files and Outlook attachments. If your total Microsoft cloud storage is over quota, whether from files in OneDrive or attachments in Outlook, Microsoft blocks Outlook from sending and receiving email, even if your mailbox shows plenty of free space. This is called Microsoft Unified Storage.
To check: go to Settings → Storage in Outlook.com. The storage bar shows your combined usage across both Outlook and OneDrive. If OneDrive is the problem, delete files from OneDrive and empty the OneDrive recycle bin to reclaim the space.
📌 For work or school accounts, see if an Archive Mailbox is available. This provides an extra 100 GB. If not, only your IT administrator can raise mailbox limits in Exchange Online.
📌 Allow 24–48 hours after freeing space. Once you delete items or upgrade your Microsoft 365 subscription, the email servers can take up to 24-48 hours to recognize the new quota and restore mail flow. If you’ve cleared storage and still can’t send email immediately, the fix has likely already worked – wait and try again before repeating the cleanup steps.
Wrap-Up
A full Outlook mailbox is usually easy to fix once you know which storage limit you’ve reached. Clear the space that’s actually causing the problem, then keep unnecessary emails from piling up again. Regular cleanup or automated rules with Clean Email can help you stay below the limit and avoid another interruption to your email.
FAQs
How to check Outlook storage?
On desktop, go to the File menu, choose Info, then click on Tools, and select Mailbox Cleanup to view your storage usage. For Outlook web users, click on the gear icon in the upper-right corner to access Settings. Under General, select Storage to see how much space you’re using.
How to free up space in Outlook?
Freeing up space in Outlook can be achieved by compressing large attachments before sending them, regularly emptying your Junk Email folder, and utilizing the Cleanup Tools to remove old calendar entries and emails.
How to increase Outlook storage?
Increasing Outlook storage often requires upgrading your subscription plan for more space or diligently freeing up existing space. Tools like Clean Email can assist in managing your mailbox, helping to maximize the storage you currently have.
Is the “Your mailbox is almost full” email from Microsoft real or a phishing scam?
It’s real. Microsoft sends these warning emails automatically when your mailbox approaches its storage limit. If you’re unsure whether an email is legitimate, don’t click any links in it. Instead, go directly to Outlook.com, sign in, and check Settings → Storage yourself to see your current usage.
Why is my Outlook mailbox still full after I deleted everything?
Deleted items continue to count toward your storage quota until the Deleted Items and Junk Email folders are also emptied. After deleting emails, go to each of those folders and permanently remove everything there too. On Outlook.com you can do this from Settings → Storage → Empty folder.
I cleared my Outlook storage but still can’t send emails – why?
Two possible causes: First, if your OneDrive is full, it blocks Outlook email even if your mailbox has available space (check Settings → Storage for your combined Microsoft storage usage and clear OneDrive if needed). Second, even after correctly freeing storage, Microsoft’s servers can take 24-48 hours to recognize the change and restore mail flow.
