How to Compact OST File without Opening Outlook?

Rollins Duke   
Published: May 31st, 2023 • 7 Min Read

Overview: This write is going to explain the most searched query on the internet on how to compact OST file to decrease OST file size. Here we will describe all the possible ways to shrink your OST file of Outlook 2021, 2019, 2016, 2013, 2010, and all previous versions using manual and expert solutions.

We all know that an OST file stands for Offline Storage Table, which is used by Outlook email clients to store an offline copy of your data including emails, contacts, calendars, notes, tasks, journals, etc. But many times, happened when the OST file has reached maximum size, that may occur many errors in Outlook including:

  • Outlook performance getting slow
  • Outlook OST data may become inaccessible or OST files may be opened.
  • Synchronization errors.
  • Getting errors while sending and receiving emails
  • Outlook not responding

In these kinds of situations, it’s become important to compact OST file to reduce size. Besides saving storage space, it will help you in Outlook performance and prevent errors, that may occur due to large OST files.

Recommended: Suggestions to Fix Outlook Mailbox Full After Archiving

Manual Methods to Decrease OST File Size

There are 3 manual methods available to compact OST file without any hassle. All the methods are given below one by one in detail:

Method 1: Compact OST File with “Compact Now” Option

This is the default feature in the Outlook email client, that automatically compact OST file when the white or unused space reaches 20% of the file size. Also, you can shrink the OST file manually by following the mentioned steps:

Note: Before using this option, check the deleted items folder and restore the important email that you have deleted by mistake. Because after compacting the OST file, you can not recover OST file data and emails that have been deleted.

  1. Open an Outlook account.
  2. Click on the File >> Account Settings >> Account Settings options.

    Account Settings

  3. Open the Data Files tab and choose the OST file you want to compact.

    data file tab to compact OST file

  4. Choose Settings >> Advanced >> and Outlook Data Files Settings options.
  5. Hit the Compact Now icon and choose OK.

And your OST file will be compacted successfully.

Method 2: Clean Your Mailbox in Outlook

To compact OST files, you can also clean up your Outlook mailbox by deleting unwanted emails and folders to save your space. The steps are mentioned below:

  1. In Outlook go to File >> Info >> select Mailbox Cleanup option.
  2. Hit the Mailbox Cleanup… from the appearing drop-down.
  3. Choose “View Mailbox Size…” to see the actual size of the mailbox.
  4. Now select the one option between:
  5. Find items older than to delete those emails from a particular number of days that you don’t want to require anymore.
  6. Find items large than to delete folders that are larger than a specific size.

If your mailbox contains only important emails, and you don’t want to delete them, then follow the next method.

Method 3: Shrink OST File Archive OST Emails

You can compact OST file without deleting anything in your Outlook account by archiving your emails.

For Outlook 2021, 2019 and 2016

  1. In Outlook open File >> Tools >> Clean up old items options.

    Clean up old items

  2. Select the required folder that you want to archive.

    Select the required folder

  3. And hit the OK button.

In Outlook 2013

  1. Open Outlook email client.
  2. File > Cleanup Tools > Archive options.

And your all emails will be moved into archive folders and will save on the local computer in PST format. with this method, there is no need to delete folders manually.

Manual methods are straightforward and free, but there are some points that you must remember:

  • Outlook must be installed on your system.
  • After deleting your emails will not be recovered.

If you have added a large number of items to the archive folder, which will increase the PST file that are stored in the archive folder data. That may cause PST file corruption.

If you have an orphan OST file or you don’t want to use these manual methods, then go for the expert solution, that will compact OST file without losing or deleting any information. Also, there are many benefits of using expert solutions that are mentioned below:

Expert Solution to Compact OST Files

We are going to take the help of the best and most amazing BitRecover OST Splitter Wizard to compact and decrease the OST file size. This software is highly recommended in the market because it has end number of features to compact OST file.

The software comes with a very user-friendly interface for all technical and non-technical users. also, the software supports all types of OST files corrupted, damaged, and inaccessible OST files. the tool compacts OST file without opening an Outlook account.

Users can download the free demo version of this software into any Windows OS including Windows 11, 10, 8, 7, and all previous versions. some of the advanced features are mentioned below:

Why Expert Solution to Decrease OST File Size without Opening Outlook?

  • The software can easily load the Outlook OST file data from the connected Outlook profile from the default storage location.
  • Also, if you have orphan OST files or folders then you can use the select files and select folders option to upload the files to a compact OST file.
  • Users can split PST files via size into 2GB, 5GB, 10GB, and 20 GB.
  • Also, the software allows users to create separate PST files for each folder like if you have 500 OST files then the tool will create 500 PST for each folder.
  • Also, you can split the resultant file via Date range, To, From, Subject, etc as per your choice.
  • The software will compact OST file with complete details including emails, contacts, calendars, notes, journals, tasks, etc.
  • Also, it doesn’t affect your OST file, with maintained hierarchy and email components it will create a PST file.

Working Steps to Compact OST Files

  1. Download and install the software.

    tool to compact OST file

  2. Add the OST file manually using Select Files and Select Folders option or automatically using the “Convert Configured Outlook Mailboxes Data” option.

    Configured Outlook Mailboxes Data

  3. Enable the Use Recovery Mode option to repair corrupted OST file.

    Use Recovery Mode

  4. Check the required folders and subfolders from the screen and the Next button to continue.

    Check the required folders

  5. Select the desired location using the Browse button.

    desired location

  6. Choose the required option to split the resultant file.

    Choose the required option

  7. Apply the advanced filter option from the Split Options tab.

    advanced filter option

  8. Hit the Split option to start the process of compacting OST files.

    compacting OST files

And your compacted resultant file will be saved at the selected location in PST format.


  • Que 1: What does compacting an OST file do?

    Ans: Compacting means shrinking your OST file data, which improves the outlook performance and saves more space. Also, it prevents errors that occur due to the large size of the OST file.

  • Que 2: Why is the OST file so large?

    Ans: We all know that the OST file contains an offline copy of Outlook data, and its synchronization with the server, if mailbox and data size increase then the OST file increase, which may cause slow Outlook performance and will take unwanted storage space.

  • Que 3: Is it safe to compact Outlook data files?

    Ans: Yes, it’s safe to compact OST data files, It just compresses your OST file data.

  • Que 4: Can I shrink a corrupted OST file?

    Ans: Yes, the software comes with a Use Recover Mode option, that can easily compress the corrupted, damaged, and inaccessible OST file.

Time to Say Goodbye

Here we have explained the best methods to compact OST file without opening an Outlook email client. We have mentioned both manual methods and expert solutions. Manual methods are straightforward and amazing but they have some limitations, so I have suggested you use manual methods, in case you have certain data. And use an expert solution if you have multiple and large OST files. If you have any doubts or queries related to the tool, then you can download the software for free to analyze the performance.

Recommended: Methods to Reduce PST File Size without Outlook