What is OST File?

An OST file (Outlook Offline Storage Table) as a local "Xerox" of your email mailbox that Outlook keeps on your computer's hard drive at Outlook default installation path. When you use enterprise grade webmail services of Exchange Server in your corporate environment and to access user data you need to configure Microsoft Exchange webmail into Microsoft Outlook so every single email from the cloud every time you click on a folder. Instead, it downloads everything once into this hidden OST file which saves copy of your full mailbox.

Key Benefits of OST file:

You are working in corporate environment and your company uses Exchange environment for webmail services. You are on-boarding a flight for travelling, but you urgently need to view invoice attachment a vendor sent you yesterday. You don't have Internet connection since Outlook saved a copy in your local OST file, you can open Outlook, browse your inbox, and read your required emails perfectly fine in offline mode.

How OST file connected with Exchange Server?

The association between OST file and the Exchange Server is a relatable, both in synchronization. When you configure your mailbox in Outlook and It finds active internet connection, Outlook constantly checks the Exchange Server for incoming/outgoing updates.

  • • If someone email, It routes through Exchange server catches it and immediately pushes a copy down to your local OST file.
  • • If you delete/update an email or move emails into any folder on your laptop, Outlook tells the Exchange Server to do the exact same thing to your mailbox in the cloud.
The OST file is connected with specific Exchange user account and the specific user machine where that created it. Because of security encryption, you cannot just copy an OST file to another computer and double-click to open it.

Important: Do not delete OST file from your pc after disconnected from Exchange server as it might possible your server administrator do not keep your data on server so your data is only saved on your pc in offline mode.

What happens when Exchange Server is Unavailable?

When the Exchange Server permanently goes down due to a server crashed or malware/ransomware attack OST automatically switches to "Orphan" mode and Outlook won't allow to access/Open your OST file.

  • • What task user CAN do: After crashing and got disconnected from Exchange Server your webmail data is stored locally in OST file so you can keep your ost file at safe place.
  • • What task you CANNOT do: You can't able to read any of your webmail data. After disconnection from server your OST losing its digital cryptographic key and become inaccessible. Your data is safe at your end but it is not accessible in any application.

    • Why User Want to Open OST file Without Exchange

    This is where things usually get massy. An OST file requires a live communication connection to its original Exchange to open the webmail data, users get completely blank and locked out of their data if that account disappears. This is the most real-world problem when user want to access their webmail but due to disconnection of Exchange server it got inaccessible.

    • • The Exchange server crashed permanently: The company server died, and there is no backup besides the employee's local computer file to access their emails data.
    • • Accidental deletion of User profile: An IT admin accidentally deleted a user's mailbox from the server, and the local OST file is the only remaining copy of years' worth of business communication and want to open your important emails data.

      • Pro Tip: A server administrator can organize the webmail data in Exchange server and by default It saves all users mailboxes information in EDB format which can by read by any third party application and all users data can be accessible without Exchange server environment at one place.

      Solution - How to Open OST File

      If the original Exchange server sync is gone, Outlook can't open an OST file directly. If you try to import it via File > Open & Export, Outlook won't show you any option to import/open it. To actually open it and get your data back, we have the real solutions:

      • • Solution A: Outlook doesn't provide direct option so you can use our OST Converter to preview OST file data without using Outlook/Exchange or third party application.
      • • Solution B (If you want to again use Outlook): You need to convert your OST file into PST format. A PST file is a outlook readable format that can be opened on any computer running Outlook, completely isolate of a server. To do this, you need a specialized OST to PST Converter tool.
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      Steps to Use OST Converter

      • ✅ 1. Download and Install OST Converter to open OST files on your system without Outlook. Run the tool as administrator.
      • ✅ 2. Select the OST File: Launch the converter software and click Browse or Select File to navigate to your hidden local folder (usually found under C:\Users\Username\AppData\Local\Microsoft\Outlook).
      • ✅ 3. Scan and Preview: Let the software scan the file. Our tools will show you a human-readable tree layout of your mailbox (Inbox, Sent Items, Contacts) right inside the software window so you can verify the data is there.
      • ✅ 4. Choose Export Format: Select PST as your output format (though many tools also let you export directly to PDF, EML, or HTML).
      • ✅ 5. Convert: Choose a destination folder on your computer and hit Convert / Save.
      • ✅ 6. Import into Outlook: Once done, open Microsoft Outlook, go to File > Open & Export > Open Outlook Data File, and select your newly created PST file to view all your emails.

      Frequently Asked Questions

      Ans.No. there is no such option provided by Microsoft or Outlook itself and renaming the file extension (outlook.ost to outlook.pst) also will not work. You need third party tool like our OST to PST Converter to perform this task seamlessly.

      Ans. By default, Windows hides it, but you can find it by pressing Windows Key + R, typing %localappdata%\Microsoft\Outlook into the box, and hitting Enter.

      Ans. No. This is the main feature of our tool that it remains the file data intact and when migrate data from OST to PST file you will get exact data structure with all email folders/contacts/calendars/tasks etc.

      Ans. Yes, of Couse our product is not only built for Outlook, you can convert your OST file data to other format like EML/MSG/MBOX/PDF which you can open in any other email client and Adobe reader to view your emails data.

      Tags: OST to PSTOpen OST fileExchange ServerEmail MigrationOST fileOST converter