How to fix Microsoft Outlook error message: 'Mailbox size limit exceeded'

It’s common for Outlook users to encounter the error message ‘You have exceeded the size limit on your mailbox’. The message is displayed as a warning notification to inform users that they have exceeded the storage limit for their mailbox, i.e., the Outlook mailbox is full. 

You have exceeded the size limit on your mailbox

Note: Even if you don’t receive a warning, your Outlook PST file might become so large that it slows down Outlook’s performance. Also, as PST file exceeds the maximum size limit, the propensity for data corruption increases exponentially. If your PST file gets corrupt, use Stellar Repair for Outlook to repair the PST file with precision and speed.

Possible Reasons Behind Exceeded Outlook Mailbox Size Limit

Following are some situations that may increase Outlook mailbox size beyond its permissible limit:

  • You’re running Outlook on Exchange server and have set mailbox size limit.
  • You are using an older version of Outlook data file (.ost or .pst)
  • Outlook PST file size has exceeded its default size (refer to the table below for PST size limit in different Outlook versions).
Outlook Versions Outlook Data File Size Limit
Outlook 2002 and older version 2 GB
Outlook 2007 20 GB
Outlook 2010 and later versions 50 GB

How to Resolve Outlook Error Message ‘Mailbox Size Limit Exceeded’?

To resolve the issue, you can choose any of these solutions:

Solution 1: Clear-out Your Mailbox by Using Outlook Mailbox Cleanup Utility

You can reduce the size of your mailbox by using the built-in Outlook Mailbox Cleanup utility. The utility provides options to de-clutter and organizes your Outlook inbox in a hassle-free manner.

Follow these steps to use the cleanup utility:

Step 1: In Outlook, click File > Tools > Mailbox Cleanup

Note: In Outlook 2007, open the Mailbox Cleanup utility by clicking ‘Mailbox Cleanup’ on the Tools menu.

Step 2: In the ‘Mailbox Cleanup’ dialog box, choose any one of the following options:

  • Option 1: Click ‘View Mailbox Size’ to check your mailbox’s size and individual folders within it. The information can help identify the folders that exceeded the mailbox storage quota and needs to be emptied.
  • Option 2: Filter content by finding items older than a certain date or items larger than a certain size.
  • Option 3: Click ‘AutoArchive’ to archive items.
  • Option 4: Click ‘Empty’ to delete all the items from the ‘Deleted Items’ folder.
  • Option 5: Click ‘View Conflicts Size’ to check Conflict’s folder size, and then click Delete.

Limitations of Mailbox Cleanup Utility

  • Using the built-in mailbox cleanup utility requires time and efforts to manage the mailbox size.
  • Manually cleaning up Outlook mailbox by using the Mailbox Cleanup tool can be overwhelming.

Solution 2: Increase Outlook Mailbox Size Limit by Modifying Registry Entries

You can increase your inbox size limit in Outlook by making changes to the registry entries in the Registry Editor. To do so, follow these steps:

Step 1: Press ‘Windows’ and ‘R’ keys together to open the Run dialog box

Step 2: In the Run dialog box, type ‘regedit’ and press Enter

Step 3: Click ‘Yes’ when prompted

Click Yes when prompted

Step 4: In the ‘Registry Editor’ window, expand the Computer folder in the left pane.

expand the Computer folder in the left pane

Step 5: Click the ‘HKEY_CURRENT_USER’ folder, and the folder’s contents will get displayed on the right-hand side of the Registry Panel.

Step 6: Navigate to the following registry path:

  • For Outlook 2007: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Outlook\PST
  • For Outlook 2010: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\Outlook\PST
  • For Outlook 2013: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\15.0\Outlook\PST
  • For Outlook 2016: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\PST

Step 7: Double-click the PST folder, and you’ll find two values in the right pane:

Double-click the PST folder

  • MaxLargeFileSize
  • WarnLargeFileSize

NOTE: if you cannot see these two values in the Registry Editor, create them manually.

For MaxLargeFileSize:

Right-click the blank space in the right pane. Click New, and select QWORD (64-bit) Value. If you’re using 32-bit Outlook, choose DWORD (32-bit) Value. Assign ‘MaxLargeFileSize’ as the filename.

For WarnLargeFileSize:

Right-click the blank space in the right pane. Click New, and select QWORD (64-bit) Value. In case you’re using 32-bit Outlook, choose DWORD (32-bit) Value. Assign ‘WarnLargeFileSize’ as your filename.

Step 8: Double-click the ‘MaxLargeFileSize’ or ‘WarnLargeFileSize’ value in the list and enter the Value data (in MB). Choose any one option under the Base tab.


Step 9: Click OK

Step 10: Exit the Registry Editor

Limitations of REGEDIT

  • Administrator privilege is required to access the Registry Editor.
  • Modifying the registry entries incorrectly can have serious implications.

Better Alternative to Manage Outlook Mailbox Size

Use Stellar Toolkit for Outlook software to effectively manage your Outlook mailbox. The software comes bundled with tools that help automate the Outlook mailbox management tasks.

For instance, PST Splitter helps in managing Outlook mailbox by splitting large-sized PST files into smaller PSTs. Also, you can choose to compress a growing Outlook data file by using the PST Compacter tool. Besides, the PST Merger tool helps clean up your mailbox by combining multiple PST files into a single file and filtering out duplicate emails. 

Read this: How to Use all 8 Segments of Stellar Toolkit for Outlook?

How Stellar Toolkit for Outlook is a better option?

  • The intuitive interface makes it quick and easy for users to perform splitting, merging, purging of duplicate emails and other Outlook mailbox management tasks – through a single platform.
  • Helps in reducing Outlook mailbox size without the hassle and risk involved in modifying the registry entries.
  • The software demo version allows users to verify the software functionality.


This post outlined the possible reasons resulting in the Outlook error message ‘Mailbox size limit exceeded.’ It also discussed the solutions to manage Outlook mailbox size, including the Outlook built-in Mailbox Cleanup utility to get rid of the clutter from your Outlook inbox. Plus, it discussed about modifying the registry entries to manage the Outlook data files (.ost and .pst) size. However, both these solutions have certain limitations. Using Stellar Toolkit for Outlook software, you can efficiently manage your mailbox in a fast, reliable, and risk-free manner.

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Charanjeet Kaur linkdin Icon

Technical writer with over 7 years of experience

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