Growing your Outlook mailbox size may require archiving old emails or adjusting your account’s storage limits. If you’ve ever seen that dreaded “mailbox full” warning, you know how frustrating it can be. Learning how to increase Outlook mailbox size is simpler than you might think, and this guide will walk you through every step.
Outlook mailboxes have storage limits that fill up fast with attachments, sent items, and old messages. When your mailbox is full, you can’t send or recieve new emails. But don’t worry—there are several ways to free up space and expand your capacity.
How To Increase Outlook Mailbox Size
Before diving into solutions, it’s important to understand what’s taking up space. Outlook stores emails, attachments, calendar items, tasks, and notes. Attachments are usually the biggest culprit. Large files like PDFs, images, and presentations can quickly eat up your allowance.
You can check your current mailbox size in Outlook. Go to File > Account Settings > Account Settings. Select your email account and click Change. Under Offline Settings, click More Settings. Then go to the Advanced tab and click Mailbox Cleanup. This shows your total size and item counts.
Check Your Mailbox Quota
Your mailbox quota is the maximum storage allowed by your email provider. For Microsoft 365, this is usually 50 GB for business accounts and 15 GB for personal accounts. Exchange server mailboxes often have smaller limits set by your IT admin.
To see your quota, look at the bottom of the Outlook window. It shows “Mailbox Cleanup” or a percentage of used space. If you see a number close to 100%, it’s time to take action.
Archive Old Emails
Archiving moves older emails to a separate data file (.pst) on your computer. This frees up space in your online mailbox while keeping your messages accessible. Here’s how to do it:
- Go to File > Info > Tools > Clean Up Old Items
- Choose a folder to archive (select a specific folder or your entire mailbox)
- Set a date—archive emails older than 3, 6, or 12 months
- Select the destination file for your archive (.pst file)
- Click Finish to start the process
Archiving is safe and reversible. You can open the .pst file anytime to view old messages. This is one of the most effective ways to increase Outlook mailbox size without deleting anything.
Delete Unnecessary Emails
Sometimes you just need to clean house. Start with your Deleted Items and Junk Email folders. Empty them regularly. Then look for large emails using the Search function. Type “size:>5 MB” in the search box to find messages over 5 megabytes.
- Delete emails with large attachments you no longer need
- Remove old newsletters and promotional emails
- Clear out Sent Items that are no longer relevant
- Empty the Recoverable Items folder (in Exchange accounts)
Be careful not to delete important business correspondence. When in doubt, archive instead of delete.
Use Mailbox Cleanup Tools
Outlook has built-in tools to help you manage storage. Go to File > Info > Tools > Mailbox Cleanup. This opens a window with several options:
- View Mailbox Size: Shows size per folder
- Find Items Older Than: Locate old messages to delete or archive
- Find Items Larger Than: Find large attachments
- AutoArchive: Set rules to automatically archive old items
- Empty Deleted Items: Permanently remove deleted messages
Use these tools regularly to stay on top of your mailbox size. Set aside 10 minutes each month to run through them.
Compress Attachments
Attachments are the biggest space hogs. Before sending large files, compress them using a tool like WinRAR or 7-Zip. You can also save attachments to a cloud service like OneDrive or Google Drive and send a link instead.
For emails you’ve already recieved, save attachments to your computer or cloud storage, then remove them from the email. This reduces the message size significantly.
Upgrade Your Mailbox Plan
If you’re consistently running out of space, consider upgrading your email plan. Microsoft 365 Business Basic gives you 50 GB per mailbox. Personal plans offer 15 GB. Exchange Online Plan 2 provides 100 GB.
Check with your IT department if you’re on a corporate account. They may be able to increase your quota without changing plans. Some organizations have custom limits that can be adjusted.
Use Online Archive
Microsoft 365 and Exchange Online offer an “In-Place Archive” feature. This is a second mailbox that appears in your Outlook folder list. It has its own storage limit (usually 100 GB or more).
To enable it, go to File > Info > Tools > Mailbox Cleanup. Click Enable Archive. This adds an archive folder where you can move old items manually or set up retention policies.
Online archive keeps your main mailbox small while preserving all your data. It’s ideal for users who need to keep everything for compliance reasons.
Empty Recoverable Items
Exchange and Microsoft 365 mailboxes have a Recoverable Items folder that stores deleted items for a set period. This folder can grow large and count against your quota.
To empty it, you need to use Outlook Web App (OWA) or PowerShell. In OWA, go to Settings > View All Outlook Settings > Mail > Message Handling. Under Recoverable Items, click Empty. This permanently removes items and frees up space.
Be careful—once emptied, these items cannot be recovered. Only do this if you’re sure you don’t need them.
Reduce Calendar And Task Items
Calendar items, tasks, and notes also take up space. Delete old calendar entries, especially recurring meetings from years past. Remove completed tasks that you no longer need.
You can also archive calendar items separately. In Outlook, go to File > Open & Export > Import/Export. Choose Export to a file, select Outlook Data File (.pst), and choose your Calendar folder. This creates a backup you can delete from your main mailbox.
Use Search Folders
Search Folders are virtual folders that show emails matching specific criteria. They don’t take up extra space because they just display existing messages. Use them to quickly find large emails or old items without cluttering your folder structure.
Create a Search Folder for large messages: Folder > New Search Folder > Create a custom Search Folder > Criteria > Advanced > Size > greater than 5 MB. This helps you identify space hogs.
Set Up AutoArchive Rules
AutoArchive automatically moves old items to an archive file based on rules you set. This runs in the background, so you don’t have to remember to do it manually.
Go to File > Options > Advanced > AutoArchive Settings. Check “Run AutoArchive every X days.” Set the default archive file location. Choose how long to keep items before archiving (e.g., 6 months). You can also set per-folder rules by right-clicking a folder, choosing Properties, and going to the AutoArchive tab.
Consider Third-Party Tools
Several third-party tools can help manage Outlook mailbox size. Tools like MailStore, CodeTwo, or SysTools offer advanced archiving, deduplication, and cleanup features. They are useful for power users or businesses with large mailboxes.
Be cautious when using third-party tools. Always backup your data first. Stick with reputable vendors to avoid security risks.
Prevent Future Overload
Once you’ve freed up space, take steps to keep your mailbox lean:
- Delete emails immediately after reading if not needed
- Use cloud storage for attachments instead of email
- Unsubscribe from newsletters you don’t read
- Set up rules to automatically delete or move certain emails
- Regularly empty Deleted Items and Junk folders
- Schedule monthly mailbox cleanup sessions
These habits will help you avoid hitting your limit again. A clean mailbox is faster and easier to search.
Common Mistakes To Avoid
When trying to increase Outlook mailbox size, avoid these pitfalls:
- Deleting emails without backing up first—you might lose important data
- Ignoring the Recoverable Items folder—it can hold gigabytes of data
- Using PST files on network drives—they can become corrupted
- Not compressing PST files after archiving—they don’t shrink automatically
- Forgetting to empty Deleted Items after archiving—space isn’t freed until you do
Take your time and follow each step carefully. Rushing can lead to data loss.
When To Contact Support
If you’ve tried everything and still can’t free up enough space, contact your IT admin or email provider. They can:
- Increase your mailbox quota
- Enable online archive
- Run server-side cleanup tools
- Migrate you to a larger plan
For Microsoft 365 users, the admin can adjust storage limits in the Exchange Admin Center. This is often the quickest solution for persistent space issues.
Frequently Asked Questions
What Is The Maximum Size For An Outlook Mailbox?
For Microsoft 365 business accounts, the default limit is 50 GB. Personal accounts have 15 GB. Exchange Online Plan 2 offers 100 GB. On-premises Exchange servers vary by configuration.
Can I Increase Outlook Mailbox Size Without Deleting Emails?
Yes. Archiving to a PST file or using online archive preserves all your emails while freeing up space in your main mailbox. You can also upgrade your plan for more storage.
Why Does My Outlook Say “Mailbox Full” Even After Deleting Emails?
Deleted emails go to the Deleted Items folder and still count toward your quota. Empty Deleted Items and Recoverable Items folders to actually free up space. Also check for large items in Sent Items and other folders.
How Do I Check My Outlook Mailbox Size In Microsoft 365?
Go to Outlook Web App, click Settings (gear icon) > View All Outlook Settings > General > Storage. This shows your total usage and breakdown by folder. In the desktop app, use Mailbox Cleanup under File > Info > Tools.
Is It Safe To Use Third-party Tools To Increase Outlook Mailbox Size?
Some tools are safe, but always backup your PST files first. Use reputable vendors and read reviews. Avoid tools that require full access to your email account or request your password.
By following these steps, you can effectively manage your Outlook storage and avoid the frustration of a full mailbox. Start with archiving old emails and deleting large attachments—these two actions alone can free up significant space. Remember to maintain good email habits to prevent future issues. If you need more capacity, consider upgrading your plan or enabling online archive. With a little effort, you’ll have a clean, efficient mailbox that works for you.