How to Fix Large OST File Performance Issues?

In this article, we will share all tried and tested methods to fix Large OST File performance issues in Outlook, prevent future slowdown and offer a smooth management of your mailbox by using OST to PST Converter. Whether you are an IT admin or a regular user these shutdowns will help you to optimize Outlook performance without risking your data.
The issue becomes more critical when Outlook takes so long to load data or becomes unresponsive during searches or synchronization. If you’re experiencing these symptoms, it’s likely due to the OST file not reducing.
Outlook users often rely on OST files to access their emails, contacts and calendars when offline. However, over time, these files can grow excessively large especially in enterprise environments or accounts with heavy media usage. A large OST file can significantly impact Outlook performance, causing slow startup, lagging, freezing and even application crashes.

Understanding OST File Size Limits

Outlook stores mailbox data locally when connected to Exchange, Microsoft 365 or IMAP accounts. While this allows for offline access and faster data retrieval, the size of the OST file can grow rapidly especially in accounts with high volumes of emails, attachments, calendar items and shared folders.
Default OST File Size Limit by Outlook Version

• Outlook 2007 : upto 20 GB.
• Outlook 2010, 2013, 2016, 2019, and Microsoft 365: upto 50 GB.
• Custom limits: IT admin can increase these limits through Windows Registry tweaks.

Why the Limits Matters?

• Outlook requires more time to index and load mailbox contents.
• Synchronization with the mail server may lag or time out.
• System resources as RAM and CPU may be overused.
• The risk of corruption and application crashes increases.

Causes of Large OST File Performance Issues

• Overtime, as emails, file attachments, meetings and reminders pile up, the OST file increases in size rapidly. High-volume mailboxes, especially those in folders containing thousands of messages, are prone to slowdowns.
• Many users store years of emails in their primary mailboxes without organizing and deleting data. Lack of rules, folder organization or mailbox quotas can contribute to rapid OST file growth.
• Without regular archiving or automated cleanup processes, Outlook continues to store everything locally. This not only loads OST files but also makes Outlook slower during searches and synchronization.

Methods to Fix Large OST File Performance Issues

If your Outlook is lagging or frequently freezing, its like due to bloated OST file. Try these proven methods to restore performance and reduce OST file size.

Method 1. Archive Old Emails and Items

1. Go to File and click on Clean Up Tools.
2. Choose the folder to archive.
3. Set the date to move older items.
4. Set destination for archived data.

Method 2. Compact OST File

1. Navigate to file and click on Account Settings.
2. Choose Data Files and select your OST file.
3. Click on Settings and press on Advaned.
4. Select Outlook data file settings and click on Compact Now.

Method 3. Use Sync Slider to Limit Cached Data

1. Go to file and click on Account Settings.
2. Press on Email and hit on Change.
3. Use the slider to reduce cached mail to 3-6 months.
4. Outlook will sync less local data, decreasing OST file size.

Method 4. Disable Unnecessary Add-ons

1. Add-ins can slow down Outlook, especially when handling large data files.
2. Go to file and click on options.
3. Press on Add-ons and navigate Next to manage COM add-ons.
4. Uncheck non-essential add-ins and relaunch Outlook.

Method 5. Increase OST File Size Limit via Registry(Advanced Users)

1. Press Win+R and enter regedit to open Registry Editor.
2. Navigate to HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\PST(Add or modify version).
3. Add or modify MaxFileSize(in bytes) or WarnFileSize as required.

Method 6. Create a New OST File

1. Close Outlook completely.
2. Navigate to: C:\Users\Admin\AppData\Local\Microsoft\Outlook
3. Rename or delete OST file.
4. Relaunch Outlook to auto create fresh OST files from the mail server.

Professional Method to Fix Fix Large OST File Performance Issues

If your OST file gets large as recommended by Outlook then we recommend you to choose RecoveryTools OST Converter as it allows to divide large OST files into smaller OST files with maintained data as appears in the source file.

1. Download and open automated software on your system.
2. Click on configured Outlook mailbox data as needed.
3. Choose mailbox data as you want in a split file.
4. Select destination path and select PST file.
5. Now, chooose PST file size and change language as needed.
6. Select advance setting and press Split to start fixing large OST file performance issues.

Benefits of Automated Approach

• This software allows you to convert OST to PDF, EML, MBOX, HTML and 25+ Export feature.
• It also helps you when OST reached maximum size.
• You can also use filter options such as date range, from, to, subject, size, separate PST per user. Export only selected Outlook items, create error log any many more as per needed.
• This software offers a user-friendly interface to easily perform by any professional or individual users.
• With this wizard, you can also import OST to Outlook, Gmail, Microsoft 365, and all IMAP Supported email server.

Conclusion

In this guide, we have shared the top 7 effective methods to fix Large OST File Performance Issues by manually and using an automated approach. If the manual approach does not work. We recommend you to opt for an automated approach as it offers fully maintained results and no risk of data loss.