Friday 29th August 2025

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How to Split Large OST File Without Data Loss? Complete Guide
Email Conversion, How to, Outlook

How to Split Large OST File Without Data Loss? Complete Guide

Shella Negs

Outlook users are aware of the OST file and its uses. This file is helpful for users to access their email in offline mode. However, as time goes by, your mailbox size grows, and with that OST file size also increases. This oversized OST file can cause issues – slow Outlook performance, data corruption, and many other issues. To avoid all these situations, it is best to split a large OST file without any data loss.

Here in this post, we will discuss the simple and secure way to reduce OST file size into small parts without affecting your data. Whether the OST form Outlook 2021, 2019, 2016, and other older versions, here is the solution. Before that, let’s check out the issue you can face with a large OST file.

Why is it Important to Compact Large OST File?

With a large OST file, you can face various issues, some of the common ones are –

  • Slow performance: With an oversized OST file, you can face the slow Outlook performance issue. An increased amount of data will take a lot of time to open, thus it is necessary to split large OST file.
  • Data Corruption: Since the OST file is prone to corruption, it is possible that the large OST file can be damaged beyond recovery. Compacting the OST file into small-sized files is the best option.
  • Sync errors: If your OST file is large in size, then when you make a change to the OST file, it can cause synchronization issues with Exchange/Office 365.
  • Difficult management: Managing an oversized OST file is a difficult task. For better management, you can break large OST file into smaller parts.

How to Split Large OST File Manually (For Free)?

Here in this post, we will discuss two manual solutions to compact large OST file. However, noted that this solution will be beneficial if you are using the active Outlook profile from which the OST file is generated. Let’s check out both of them –

Option 1: Using the Outlook Export Option

  1. Open Outlook and click on the File option.
  2. After that, Select Open&Export >> Import/Export/
  3. Export to a File >> PST File.
  4. Choose the important folders.
  5. Browse the saving location and save the .pst file.

Here you takeout OST emails to PST with only important data.

Option 2. Use the Auto Archive Feature

Outlook has an auto-archiving feature that allows users to save  OST emails into PST file. Here are the steps –

  1. Go to File > Options > Advanced > AutoArchive Settings.
  2. Set a time period (e.g., archive items older than 6 months).
  3. Outlook creates smaller PST archives automatically.

Here are a few solutions to compress the large OST file into smaller parts. However, this method works with an active Outlook profile and is suitable for small amounts of data.

Expert Solution to Reduce OST File Size| No Data Loss

With the BLR OST File Converter Tool, you can easily reduce the oversized OST file in a few simple clicks. The tool will effortlessly split large OST file into smaller .pst files without any data loss. All you need to do is add the large OST file and choose PST from the export option. After that, select the split the result PTS option and choose the size of the data file. This OST Splitter Tool will start compacting your large OST file in a few seconds.

Most importantly, this software supports OST file from Outlook 2021/2019/2016 and all other versions. Download the demo version of the software to know how it works.

download-free -software

Here are the steps to Split Large OST File

  1. Run the BLR OST Splitter Tool on your system.
  2. Click on Add file option and browse the large OST file, click Next.Add the large OST file
  3. Choose the email folders from the OST file.Choose email folders
  4. Select the PST from the export options.Split Large OST File
  5. Click on Split resultant file and choose the file size.Select the size of splitted file
  6. At last, browse the saving location and hit the Export button.split large OST file

Done! Here, you break a large OST file into different small files without any data loss.

Why Choose BLR OST Splitter Tool Over Manual Solution?

  • With this automated tool, there are various outstanding features, including –
  • Even if the OST file is corrupted or damaged, this tool will split it without any data loss.
  • Additionally, you can also export OST file to PDF, CSV, EML, and many other file formats.
  • Preserve email key elements and attributes – to, from, cc, attachments, inline images, and all other.
  • Filter option to split OST file by years and date & time as well.
  • Maintain email folder hierarchy and structure while splitting large OST file.
  • Option to save the split file by size (in GB or MB).
  • Using this tool, you can also move the OST file into Office 365, Gmail, and many other file formats.
  • A free demo version is also available to see how the tool works to reduce OST file size.

Safety Measures to Prevent Oversized OST File

  • Instead of piling a lot of emails into a single OST file, export them into PST file and reduce its size.
  • If your inbox or any other folder has unimportant emails, then delete them regularly.
  • To handle the oversized OST file, always trust a reliable tool to break large OST file.
  • Use the Outlook archive or compact feature so that the OST file doesn’t get oversized.

Conclusion

In this post, we discuss the best ways to split large OST file without any data loss. You can either use the manual techniques or the automated tool; the choice is yours. However, when you are handling the orphan and oversized OST file, then rely on the best OST Splitter Tool. One such tool offered by BLR Tools that will effortlessly manage oversized OST file without any hassle.