How To Reduce OST File Size In Outlook 2019/2016/2013?

Summary- This article provides a detailed method to reduce the OST file size in Outlook 2019/2016/2013. It explains the step-by-step manual process to reduce OST file size. Additionally, you also come to know about professional software that allows you to reduce oversized OST files.

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An OST is an offline storage file of Outlook that saves the mailbox data in offline mode. You can create emails and other data items in an OST file without an internet connection. The OST file format consists of a Personal folder file (PPF) that stores emails, contacts, calendars, etc.,

The OST file contains the following components:-

  • Entire mailbox data including emails, contacts, calendars, notes, tasks, journals, etc.,
  • Hidden items and Public folder favorites
  • Shared folders from additional mailboxes associated with the exchange account.

Why OST File is Oversized?

Due to the large quantity of information sometimes, the OST file turns out to be oversized. It’s hard to manage oversized OST files and this leads to damage and corruption to the existing files which make Outlook data suffer. The storage capacity of a file depends on the version of the Microsoft Outlook application. Now let’s discuss the regular maintenance to reduce the size of an OST file.

Maintenance to Reduce the Size of OST File In Outlook

Regular maintenance of the mailbox folder is necessary to keep the data safe and secure. If the mailbox folder is not maintained regularly then there may be chances of data corruption and damage. Following are some measures to check the size of the OST file:-

  1. Delete unwanted emails and other mailbox items.
  2. Regularly empty the trash and spam folder to reduce OST file size.
  3. Perform hard deletion of data items if they need to be deleted from the mailbox.
  4. Ensure regularly that mailbox folders are compacted.

These are some reasons because of which regular maintenance of the OST file in Outlook is required. Now, move forward to the best solution to reduce the size of an OST file.

Methods to Fix Oversized OST Files

Here, we will discuss the best methods to reduce OST file size. These methods are easy to perform and provide effective and reliable results.

  • Disabling all Add-Ins In Your Outlook
  • Archive OST file Data
  • Compact the OST file Size
  • Microsoft Outlook reduce OST file size Professionally

Disabling all Add-Ins In Your Outlook

Add-ins in Outlook creates many issues for its users. So, to avoid such dysfunction, disabling the

Add-ins is a great option. Perform these steps to disable the Add-Ins:-

  1. Open Microsoft Outlook, go to the File menu, select the required option then click Add-Ins.
  2. click on add in
  3. Then under view and manage Microsoft office Add-ins choose the COM Add-in and click Go.
  4. hit on go
  5. Now unselect all the Add-ins that are not currently in use and select Ok.
  6. click ok

Archiving OST file Data

By archiving the unrequired OST files you can clear some space, and as a result, it reduces your OST file size. Archiving the oversized OST files free up space and prevent file corruption or file damage.

Steps to Archive the OST file Data

  • Open Microsoft Outlook and click on the File tab.
  • Click cleanup tools, then select mailbox cleanup.
  • click on cleanup tool
  • Now, these two options are available for you;-
  • Move the older items in the mailbox to an archive folder by clicking on the Auto Archive option.
  • Click on the empty option and delete items from the deleted items folder.

Compact the OST file

To compact, the size of the OST files follow these steps:-

  1. Delete unnecessary items that need not be compacted or saved in the mailbox.
  2. Open folder list view, and in the Navigation pane, right-click on the folder, click Deleted items and click Empty folder.
  3. In Microsoft Outlook, click on the File tab, and from the Account, setting select the Account Setting option.
  4. Choose the Data File tab, select the data file that needs to be compacted and click Settings.
  5. click on cleanup tool
  6. In the opened dialogue box, click the Advanced tab and then click Outlook Data File Settings.
  7. In the Outlook Data File Settings dialogue box, click Compact Now, the final step.

These are some manual methods to reduce the size of an OST file but these methods have some limitations such as sometimes if an OST file gets corrupted or damaged due to their oversize then you may lose your data. To avoid these types of limitations I would recommend you to use another method to reduce OST file size.

Professional Solution to solve the problem of Oversized OST file

The SysInfo OST splitter software is a risk-free utility to use. It splits the Oversized OST file into multiple parts by date, size, email category, etc. This software provides many salient features to its professional and non-professional users. It is 100% reliable and reduces the size of OST files in very little time.

Some of the advanced features of Professional Software are:-

  • Splits large size OST files: The OST splitter provides the option to break the large size OST file by Date, Name, Size, Email category, Year.
  • Provide option to repair corrupted files:- This tool provides the option to repair the corrupted and damaged files before splitting the large-sized files.
  • Outlook Installation is not required:- Users can easily split the OST files even without Installing Microsoft Outlook on their PC.
  • Split the newly created OST file and archived OST files:- This tool also provides the option to split the newly created OST file and archived OST files to its various users.
  • Provide a new folder to save OST files:- After splitting the Oversized OST files. This tool provides the new folder option to save the resultant OST data file.


This blog provides the causes why OST files get oversized and the solution to reduce OST file Size. In this, you will get three manual methods to fix oversized PST files. You can also go for the Professional Software for more reliable and effective results.

Frequently Asked Question

What causes OST files to be large?

OST file contains emails, calendars, journals, contacts, tasks, assignments, and due to the large quantity of information, sometimes, the OST file turns out to be oversized. Thus, it is hard to manage oversized OST files which lead to damage and corruption.

How do I find the OST file size?

These are some steps to find the OST file size:-

  • Right-click on the folder you want to check then select Data File Properties. In Microsoft Outlook select Properties.
  • Now, select the size of the folder.
  • The folder Size box shows the folder size and its subfolders in kilobytes.

About The Author:

I'm a content writer in the field of Email Migration, Data Recovery, Email backup, and File Management. I started this writing career two years back. I think the vast range of information in this industry is the reason I am so fascinated to read about the newer techniques and technology.

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