How to Reduce OST File Size with OST Splitter Tool?

In this article, we will discuss the need to reduce OST file size and the possible solution to break the size of large OST into smaller ones.

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Summary: Outlook is a popular email managing program developed by Microsoft. It creates OST files that store data locally and help users to view emails in an offline mode. As time flows, your OST file becomes large and heavy, which is the main reason to show errors. The capacity of OST file size differs from version to version of MS Outlook. Here is the list of capacity according to installed versions of MS Outlook:

MS Outlook 2002 and before 2 GB
MS Outlook 2003 and 2007 20 GB
MS Outlook 2010 and later 50 GB

Why do we Need to Reduce OST file Size?

Sometimes, OST files get large due to a massive amount of mailbox data, and as a result, it corrupts or damages your OST file. There is also a possibility of slow synchronisation and many more Outlook errors. Some common issues that allow you to Microsoft Outlook reduce OST files size are

  • MS Outlook crashes or hangs.
  • Retrieving data from the exchange server.
  • Accessing problem with the OST file.
  • Cannot add additional data to existing exchange .ost file.
  • Delay in the synchronisation process.

Now, To safeguard your data from corruption or loss, you must reduce the OST file size using the methods provided here.

Ways to Reduce the size of an Offline data file (.ost)

There are several methods to reduce the size of an OST file. These methods are tested and reliable and will not cause any harm to your data.

Use the MS Outlook In-built Mailbox Cleanup Utility

This method involves erasing old or unwanted files to reduce the OST file size. Follow these simple steps to clean up your mailbox in MS Outlook:

  1. Open MS Outlook and Click on the File tab.
  2. Click Tools >> Mailbox Cleanup.
  3. click account setting
  4. Tap on Empty, then press Close to end the process.
  5. tab on empty
  6. You can view your mailbox size before and after the cleanup procedure.

Disable COM Add-ins

Add-ins are the extra programs that outlook does not provide. It can increase memory and take up space in the OST file. Perform these steps to remove or disable the Add-ins in Outlook:

  • Open Outlook and tap the File menu.
  • Go to Options.
  • go to options
  • Click on Add-ins at the bottom of the list.
  • img src=”” alt=”click on addin”
  • Choose COM Add-ins and press the Go button.
  • img src=”” alt=”choose com add ins”
  • Deselect all the checkboxes and click OK.
  • img src=”” alt=”click ok”

If Both these methods do not resolve your issue of ‘How to Reduce OST file size’, then hop on to the next one.

Compacting OST files

Outlook provides an internal feature to shrink your OST or PST file data. This method is not complex; make sure you follow them correctly to prevent data loss:

  1. Open File in MS Outlook.
  2. Click Account settings >> Account settings.
  3. click account setting
  4. Tap on Data files and choose your preferred account.
  5. tab on data file
  6. Then, click the Settings button.
  7. click on setting button
  8. Press the Compact Now button to Reduce the OST file size.
  9. press compact now

Archive OST and PST files

In this method, Create an archive folder to backup your OST or PST file using the internal feature of Microsoft Outlook.

  1. Open File tab.
  2. Click the Tools button and choose Clean up old items.
  3. click on tool and cleanup old item
  4. Tick Archive this folder and all subfolders.
  5. click archive this folder
  6. Now, select the folder you want to archive.
  7. Browse the location you wish and Tap OK.
  8. browse location

Professional Solution to Reduce OST file size

This is the ultimate method to reduce your OST file size in an instant. Use the OST File Splitter developed by SysInfo. This software allows users to split OST files into smaller files with different filters like Split OST file by size, date, sender’s name, and folders. It also offers some features such as Ignore duplicate mails, password protection, and many more.

Step By Step Guide to Split OST file using this software:

  • Download & Install SysInfo OST Splitter Tool and Run as administrator.
  • Use the Add Files button to add your OST file.
  • Click Next.
  • Now, Tick the desired filter and Tap Next.
  • You can enter the PST file size in MB or GB.
  • After using the features, click on the Split button to end the process.


In this article, we explained the need to reduce the size of the OST file and the manual ways to do it yourself. If you are a novice user and don’t have technical knowledge, then opt for the expert solution and save your time from the complex process of the manual method.


How do I fix the Outlook data file has reached the maximum size?

→ To fix this error, you can reduce the OST files size using SysInfo OST Splitter Tool. Also, If your OST file is being corrupted then try using the OST Recovery Tool.

How to reduce OST file size?

  1. Open Files tab in Outlook.
  2. Click on Tools >> Mailbox Cleanup.
  3. Tap on Auto Archive.

About The Author:

As a content writer, I specialize in Email Migration, Data Recovery, Email Backup, and File Management. I have been writing professionally for two years now. There is so much information available in this field that I am intrigued by the newer technologies and techniques.

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