How to Compact OST File – Step by Step Solution

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OST files are utilized for all the offline work of MS Outlook. If you are also facing the oversized OST issue due to huge data in them or want to compress or compact OST file, then read this post. You will find all the relevant methods to compact OST files. Additionally, further OST info has been shared to prevent you from this problem.


Microsoft Outlook stores its data in two file formats, i.e., OST and PST. However, the usage and requirement of both these formats are quite different. PST (Personal Storage Table) is required for online email transmission, while the OST (Offline Storage Table) is used while working with Outlook in Offline mode. If a stable internet connection is not available, you can work on the OST files that increase their sizes immensely. Hence, it gives rise to the need to compact OST files.

In this blog, we will be talking about the methods using which you can compact a .ost file. These files gain size as you keep on using them as more and more data is stored substantially. This data consists of numerous emails, attachments, contacts, etc.

The Outlooks starts to have performance issues as the size of the OST files is increased. It affects the transmission of emails as well. Earlier, the maximum size that an OST file could have was 2GB. But, now, it has been increased to around 50 to 60GB for each OST file.

Now, let us move towards the solutions to compact the OST file. But before that, we should be familiar with the need to compact OST files.

Why do we need to Compact an OST file?

  • The main and basic need for compacting Outlook data files is for the smooth functioning of Outlook.
  • You need to compact the OST file because huge data in these files makes them corrupt, which can result in losing all the data.
  • The MS Outlook starts to lag as you keep on storing data in the OST files. The huge size of these files hinders Outlook from opening smoothly affecting the user experience.

All the above points show us the need to compact OST files. However, if the same is not done effectively. It can lead to the below problems.

Also Read: How to Recreate OST File in Outlook 2019,2016,2013,2010,2007

Problems of Large OST Files

As we know, large OST mailbox data tends to slow down your Outlook and programs, corrupt files, distort indexing by search engines, and cause many other types of problems. Perhaps, the major and most common issues are mentioned below.

  • The data on the Microsoft exchange server starts lagging and gets stuck with a post request.
  • The download of the data from the exchange server starts to have issues.
  • The Outlook email client does not respond.
  • You cannot add additional data to an existing OST file.
  • The delay in the opening of a document is also an issue.

All the above points show us the necessity to compact OST files. Also, there are some prerequisite points that you should keep in mind before you start to compress the OST file.


Before you initiate to compress Outlook data files in Microsoft Outlook 2003, 2007, 2010, 2013, and 2016, you must meet the following prerequisites.

  • The size of the file must be a minimum of 16KB.
  • The file must have a minimum of 16KB of free space since the last time it was compressed.

Once you have taken care of the prerequisites above. Now, you can move forward towards the ways to compress OST files.

Methods to Compact OST File

You can perform the below-mentioned methods to compact OST file Outlook 2013 and other Outlook versions. All the methods are described in a stepwise manner so that you can execute them effectively.

Method 1: By Disabling all Add-ins in Outlook

  • Run the Microsoft Outlook application and hit the File tab.


  • After that, choose the Options tab from the left pane.


  • In the new wizard window, click on the Add-ins tab on the left of the window screen.


  • Now, go to the bottom of the page. Select the Go button in front of the Manage option.


  • It will open the list of all the add-ins available. Disable one by one.


This method will compact OST files and resolve the issue of oversized OST files. However, if the problem does not get solved, you can practice the next method.

Method 2: Archive the Outlook OST files

It is a simple method that will move the less important emails to another folder and compact the Outlook file. Also, you can clean up space by deleting all unnecessary emails.

  • Launch the Microsoft Outlook application and click on the File option.
  • Now, choose the Info tab from the left pane.
  • After that, click on the Cleanup Tools icon on the screen.
  • Now, you will see the following two options on the screen.
    • Auto Archive option: It allows you to move the old emails to an archive folder.
    • Empty Deleted Items Folder: It will clean up the emails that are stored in the deleted items folder.

Method 3: Compressing Outlook Data Files

The most obvious solution to compress Outlook mailbox without losing the data is to compress the OST files. It does not damage the file content but only compresses the files. Follow the steps below to compact OST files.

  • Start with deleting the unnecessary emails from the mailbox.
  • Now, open the mailbox folders in the list view and then right-click on the folders options. Press the Deleted items option followed by clicking the Empty folder option.
  • After that, open the Microsoft Outlook application and click on the File
  • Select the Info tab and then press the Account Settings
  • Here, pick the Account Settings
  • It will open an Account Settings Choose the Data File tab at the top.
  • After that, click on the data file that you want to Compress. Press the Settings
  • A new dialogue box will appear. Move to the Advanced tab
  • Click on the Outlook Data Settings It will open another new wizard.
  • At last, click on the Compact Now button, and after compressing, press OK.

You can perform all the above manual methods to compact OST files. However, all these solutions have some limitations that restrict their usability. They take a lot of time for the users to show results, and the novice users cannot easily execute them. Also, they require prior technical knowledge for proper execution.

Automated Solution

If you wish to overcome all these limitations, you can undertake another approach for resolving the OST file issue. You can convert the OST file to PST using the professional tool, OST to PST Converter Software, and then you can easily compact your converted OST files using the PST Compact Tool. It is a direct method to compress or compact a PST file of any size.


Oversized OST files can cause numerous issues in the working of the MS Outlook application. You have an option to compact OST files and save yourself the trouble. To compact ost file, you can follow the manual methods mentioned above. Furthermore, you can also opt for an alternate third-party tool to resolve your issue.

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