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

January 16, 2020

It’s common for Outlook users to encounter error message ‘Mailbox size limit exceeded’. The message is displayed as a warning notification to inform users that their mailbox size has exceeded the limit.

The error message looks similar to:

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 exceeds exponentially. If your PST file gets corrupt, use Stellar Repair for Outlook to repair the PST file with precision and speed.

What Causes Outlook error message ‘Mailbox size limit exceeded’?

There could be several situations that may increase Outlook mailbox size beyond its permissible limit. Some of them are listed as below:

  • 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
Outlook Versions Outlook Data File Size Limit
Outlook 2002 and older version 2GB
Outlook 2007 20GB
Outlook 2019 and later versions 50GB

How to Resolve Outlook error message ‘Mailbox size limit exceeded’?

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

Solution 1 – Clear-out your mailbox by using Mailbox Cleanup Utility

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

Follow these steps to use the cleanup utility:

Step 1: Open the Mailbox Cleanup window:

For Outlook 2007

Click File > Tools > Mailbox Cleanup

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

Option 1: Click ‘View Mailbox Size’ to check the size of your mailbox and individual folders within it. This information can help in identifying the folders that about to exceed 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 the size of your Conflicts folder, 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 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

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

Step 5: Click the ‘HKEY_CURRENT_USER’ folder, and the folder’s contents will get displayed in 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:

  1. MaxLargeFileSize
  2. 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. But, if you’re using 32-bit Outlook, choose DWORD (32-bit) Value. Assign ‘MaxLargeFileSize’ as name to the file.

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 name to the file.

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. In addition, the PST Merger tool helps in cleaning up your mailbox by allowing you to combine multiple PST files into a single file and filtering out duplicate emails.

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.
  • Demo version of the software is available to help users verify the software functionality.

For more information about using the Stellar Toolkit for Outlook, refer to this link.


This post outlined the plausible causes resulting in Outlook error message ‘Mailbox size limit exceeded.’ Also, it discussed about 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. In addition, it discussed about modifying the registry entries to reduce the Outlook data file (.ost and .pst) files size. However, both these solutions have certain limitations. By using Stellar Toolkit for Outlook software, you can efficiently manage your mailbox in a fast, reliable and risk-free manner.