How to Increase Outlook Mailbox Size?

Is your Outlook mailbox constantly showing “Mailbox Full” errors? If so, it's time to take action. Whether you're using Outlook for personal or business use, running out of space can disrupt your email flow and productivity. This guide will walk you through how to increase Outlook mailbox size and effectively expand Outlook storage capacity using multiple reliable methods.

Why Does Outlook Mailbox Get Full?

Prior to expanding the mailbox, you should be aware of what is causing the problem:

• Large email attachments will build up over time.
• Sent, Deleted, and Junk folders contain unnecessary emails.
• You have no auto-archiving that keeps your older emails active in the main mailbox.
• The default storage limit in Outlook is contingent upon your Outlook plan or license.

How to Check Current Mailbox Size in Outlook?

For Outlook Desktop:

1. Open File Tools Mailbox Cleanup.
2. Click on View Mailbox Size for total size and breakdown by folder.

For Outlook Web / Office 365:

1. Click on Gear icon View all Outlook settings.
2. Navigate to General Storage for your current usage.

Best Methods to Increase Outlook Mailbox Size

There are many ways to expand Outlook storage capacity, which can help Outlook perform better and give the best results. Methods given below:

1. Use Outlook’s Cleanup Tools
2. Use Online Archive items
3. Compact the PST/OST File
4. Delete Large Attachments
5. Create Multiple PST Files
6. Use Third-Party Tool

Let's discuss them one by one quickly:

#1: Use Outlook’s Cleanup Tool

Method: It is used to delete duplicates based on their size and their old items

Steps:

1. Mailbox Cleanup:
   Go to File Tools Mailbox Cleanup to:

• View mailbox size
• Find items older than a specific date
• Locate large emails

1. Empty Deleted Items and Junk Email folders:
   Permanently delete emails that are no longer needed.

2. Find items older than:
   Identify and delete old messages that are just taking up space.

Read more: if your Outlook cleanup tool not working, then go through this article.

#2: Use Online Archive items (for Microsoft 365/Exchange Users)

Method: Automatically move older emails to a cloud-based archive mailbox to free up space in your primary mailbox.

Steps:

1. Enable from Admin Centre:
   Your Microsoft 365 or Exchange admin needs to enable the Online Archive from the Microsoft 365 Compliance Centre.

2. Auto-Archiving:
   Once enabled, emails older than a certain age (default is 2 years) are automatically moved to the archive.

3. Expands Automatically:
   The archive mailbox grows as needed, so you never run out of space.

#3: Compact the PST/OST File

Method: Shrink the data file size by removing unused space left after deletions.

Steps:

1. Navigate to File Account Settings Account Settings
2. Click the Data Files tab.
3. Select your PST/OST file and click Settings.
4. Choose Compact Now.

#4: Delete Large Attachments

Method: Identify and delete emails with bulky attachments to instantly free up space.

Steps:

1. In Outlook’s Search bar, type:
   hasattachments:true

2. Sort the results by size to see the biggest files at the top.

3. Options:

• Delete the entire email if it’s no longer needed
• Save the attachment to your computer or cloud storage
• Remove just the attachment (Right-click "Remove Attachment")

#5: Create Multiple PST Files

Method: Manage large mailboxes by splitting them into smaller, more organised groups.

Steps:

1. Go to File Account Settings Data Files Add...
2. Create a new PST file.
3. Manually drag and drop older emails or folders into this new file.

Note: there are many duplicates available in Outlook's mailbox which are also making the size maibox full, so try to remove duplicate emails in Outlook mailbox by using some manual methods or a professional alternative automated tool. Let's also know how we can delete similar emails in Outlook mailbox.

#6: Use Third-Party Tool

Method: Use specialised tools like SysTools Outlook Duplicate Remover to automate and optimise mailbox management beyond Outlook's built-in features.

Benefits of this Professional Tool

• Reliable Accuracy: Detects exact and partial duplicates even across Outlook folders.
• Fast Performance: Processes thousands of emails with attachments in a few clicks.
• Safe Secure: It keeps the original email data intact, which saves them from the risk of losing it.
• Ease of Use: Created for all types of users, as it has a user-friendly interface.
• Free Trial Available: To scan the duplicates before deleting, take advantage of the demo version.

You can also read about how you can remove duplicate attachments in Outlook, as it's also making your mailbox size full.

Steps:

1. Install and launch the Outlook similar eliminating Solution.

2. Click Add File Folders to upload your Outlook mailbox files.

3. It allows users to add files within folder or across folder.

4. Choose Destination to save the outcome file where you want.

5. In select item types, choose mail, task, or journal options for removing duplicates.

6. Set Specific Duplicate Criteria, such as emails, attachments, and tasks.

7. Click Next to delete duplicates in Outlook to increase Outlook mailbox size.

Troubleshooting: Still Getting “Outlook Mailbox Full” Errors?

1. Check mailbox size again after performing updates:
After updating your quota or clearing some space, you should check to see if the changes have taken effect and the mailbox size has updated in your Outlook settings. 
This means the updates you made had an effect. 
Sometimes changes in Outlook won't happen automatically without some sort of manual action.

2. Ensure you are not syncing large shared folders:
Any shared mailbox or shared calendar can take up your quota if it has a lot of content in it.
So, make sure you are not syncing shared folders that you don't need to sync in your account settings.
This way, if you do, when you check your size from your primary inbox, it looks relatively clean, but it is still part of the overall quota.

3. Check for corrupt PST/OST files:
Corrupt data files can cause reporting for storage amount to be inaccurate, and sync limitations of storage.
You can use the Inbox Repair Tool within Outlook (ScanPST.exe) to run a scan and fix potential errors, and it may not require replacement or repairing of the current file. And if the corrupted file is repaired, there will be no more issues with false reports of "mailbox full", etc.

4. Contact Microsoft support if upgraded package does not show any changes:
At times, a particular upgrade in package plan by an organisation does not automatically update the user's account on the server once that upgrade is finalised.
You can contact Microsoft support for them to check the user's limits (and verify the upgrade was successful), and to ensure there are no account-specific or sync issues.

Conclusion

In this article, we've discussed that there is more than one way to increase Outlook mailbox size and efficiently expand Outlook storage capacity, from changing registry settings to utilising the built-in Outlook tools like AutoArchive or Cleanup. For the average user, transitioning to the Microsoft 365 platform or enabling Online Archive offers indefinite relief from mailbox storage issues.

Stay organised and keep your Outlook clean, and that irritating "mailbox full" warning will be a thing of the past!