How to Fix Outlook OST File has Reached the Maximum Size?  

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If you are receiving an error message that your outlook OST file has reached its maximum size and you may be unsure of what to do next but do not worry about it because in this article we have mentioned various methods on how to resolve the error of Outlook OST file has reached the maximum size with tried and tested methods.

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OST (Offline Storage Table) file is an Outlook data file where your emails, contacts, tasks, and other data are stored.  The best part about OST file is that it allows you to work offline. This file contains data that can over time make your OST file oversized and leads to problems that you just encountered. Outlook OST file has reached maximum size, you will be seeing an error like this, if your Outlook is oversized. We have covered everything you need to know about this issue and how to easily fix an oversized OST file issue in this article. 

Why Does Outlook Show an Error, The Outlook Data File has Reached Maximum Size OST.

This issue occurs because the size of the OST file is limited. Once the OST file reaches its maximum limit you will be getting an error message- “The Outlook OST file has reached maximum size”.

How to Check the Mail Box Size in Outlook OST? 

To check mailbox size in Outlook OST follow the given steps:

  • Go to Outlook Account 
  • Choose the General Option on the screen
  • At the bottom of the screen, you can see a box showing the Storage of the Mailbox 

Ways to Solve the Issue Outlook OST has Reached the Maximum Size 

Before we go ahead and discuss ways to fix this oversized OST file issue, you need to know that the methods mentioned below will involve cleaning your Outlook data file or deleting duplicate Outlook data. However, if you are one of those who don’t want to delete anything we recommend you to take Outlook backup safely using a professional Outlook Backup Software.
Remo Outlook Backup and Migrate is an exclusive backup and migration tool that is specially built for Outlook. With this software, you can back up your Outlook data like emails, contacts, calendar, notes, and even settings. Download and try the tool now. 

Mailbox Clean up

Mailbox clean-up is a built-in tool to clean it used to trim the size of the OST file. To clean up your OST outlook account follow the below-given steps.

  1. Open your Outlook
  2. Look for the Mailbox Clean up option, usually located in the toolbar or menu of your email.
Mailbox cleanup screen

3. Select the folder you want to clean up.

find folders to clean up

4. Click on the OK or Clear All button to clean up your emails.

Archive the old data 

Archiving old data is one of the easiest methods to fix an issue of the error message The Outlook OST has reached maximum size. Follow the below given steps to Archive the old data 

  1. Open Microsoft Outlook and go to the File menu.
  2. Click on the Account Settings dropdown and select Account Settings.
Account settings screen

3. Select the Data Files

OST file folder

4. Highlight the OST file you want to archive and click Open File Location.

5. This will open the folder where the OST file is stored. Close Outlook to release the lock on the file.

6. Rename the OST file by adding _old to the end of the filename.

7. Reopen Outlook and create a new PST file by going to File and selecting New click on Outlook Data File.

8. Choose a location and filename for the new PST file and Click OK.

9. In the navigation pane of Outlook, right-click on the folder you want to archive and select Copy Folder.

10. Select the new PST file as the destination and click OK.

11. The folder and its contents will be copied to the New PST file.

12. Repeat the above steps for any additional folders you want to Archive.

13. If this method did not work, you can try the next method which does a good job of fixing an issue of an OST file error.

Compact the Data File 

Compacting the data file which is good at reducing the size of the OST file. This method can help you in resolving this issue if the OST file has reached maximum size. To resolve your issue follow the below given steps.

  1. Open Microsoft Outlook 
  2. Click on the File menu in the top left corner.
File tab screen
  1. Select “Account settings” and click on Account settings again from the bottom 
Account settings screen
  1. In the Account Settings window, Select the Data Files 
  1. Highlight the OST file you want to compact and Click on the Settings button 
  2. In the Outlook Data File window, click on the Advanced button.
  3. In the Advanced window, click on the Compact Now button.

If you are still not satisfied with this method you can try the other best method to resolve your  issue on the OST file.

Use Registry 

The registry helps windows manage and operate the computer ensuring that files are accessible it can also help you in configuring settings. To increase the maximum size of an OST file.

To use Registry follow the given below steps 

  • Move to Hkey_Local_Machines/system/Currentcontrolset/control key
  • From the Edit menu, select the new - Dword value 
  • Now enter the name as registry size limit.
  • Double-click the new entry and enter a Value in Bytes.

If all these methods did not work in increasing your OST file do not worry there is another method to get storage space which is by Splitting the Data file follow the below-mentioned method for more information.

Split the Data File 

Splitting the Data file is done to get extra storage for the OST file it is the best way to make storage for your OST file. To split the Data File follow the below-given steps 

  1. Open File Explorer on your Pc
  2. Right-click on the OST file and select Copy to create a backup copy of the original file
  3. Rename the backup copy of the OST file to a different name to avoid confusion 
  4. Open Microsoft Outlook and create a new PST file by going to file and choosing account settings clicking on data files clicking on Add 
  5. Save the New PST file in a location where you can easily access it.
  6. Drag and drop the items from the OST file to PST the files you want to split 

If nothing worked just disable your ad-in this will help you in managing your file size. Follow the other method to get storage for your OST file.

If you getting same error with PST file you can refer this article Outlook PST file has reached maximum limit

Disable ad-ins 

Disabling the ad-ins will help in clarifying the unwanted files to store in your OST file this will maintain your OST file storage.

  1. Open Outlook and click on the File menu
  2. Click on Options and then choose Add-ins
  3. In the Manage bottom select COM Add-ins and select Go
  4. Uncheck the boxes next to the add-ins you want to Disable.
  5. Click OK to save the changes 

Bonus: Alternative Methods to Reduce the Size of OST File 

This method is used for maintaining the size of the OST file instead of increasing the size of the OST file the following methods will help in keeping your OST files with maximum storage and how to maintain the maximum storage. Here are two methods that will help you in maintaining the OST file storage.

  • Ost-files contain compressed mailbox data:
    The new version of Outlook contains a mailbox compressor where that automatically compresses Outlook data files to be short so that there will not be a spacing issue it can contain more content by keeping the OST file smaller by up to 30% than its actual size.
  • Adjust the sync slider :
    Another feature of newer versions of Outlook is the Sync slider this feature allows you to adjust the size of the mail on how much size it should be you can adjust your mail size by adjusting the Sync slider.

All the above-mentioned methods do help you to reduce the size of your oversized OST file. However, to avoid this situation in the future, it is recommended to use an Outlook backup software like Remo Outlook Backup and Migrate Tool. This will definitely save you from all Outlook-related woes. Download and give this tool a try. 

Frequently Asked Questions 

What happens if your mailbox is full?

If your mailbox is full you will not be able to receive any new emails till you free the storage space. If your storage is the email will bounce back to the sender and you get a message telling you, your mailbox is full.

What is the maximum size Outlook OST file?

The maximum size of the Outlook OST file depends on the versions of Microsoft Outlook.
Outlook 2010, 2013, 2016, 2019, 2021 the maximum size of these versions is 50GB 
The Older version of Outlook is 20GB

Can Outlook OST be more significant than 50GB?

Yes, The OST files can be larger than OST files it depends on the versions of outlook you are using the new versions of Outlook can increase the size limit from 50GB to 100GB using the registry and other methods to increase the size limit of OST files.


About the Author: Tony Landry

Tony Landry is a Web Content Editor at Remo Software. He loves to write, edit, and manage content for users trying to troubleshoot and fix problems on Windows, Outlook, storage drives, and Cloud storage networks. With an aptitude that transcends writing, Tony is recognized as a Microsoft Outlook, Word, and PowerPoint expert. His comprehensive solutions…