What Is an OST File?

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An OST file (AKA “offline storage table” or “Outlook storage table”) is an Outlook data file that is created when the Outlook profile is configured with the MS Exchange server with cached mode enabled. In simpler words, the OST file is the replica of the mailbox content on the server that allows users to access the data when disconnected from the server.

The possibility of working offline is very beneficial, especially the times we encounter limited or interruptible connectivity. The good news is, that any changes done by the client or server will be updated at both ends the next time connection between them is made, which is a process called synchronization.

ost file sample

What Is an OST File?

An OST file offers a set of special folders to preserve mailbox data such as Inbox, sent mails, drafts, contacts, calendars, and more. So, even after disconnecting from the Exchange server, you can still go ahead with the task at hand. You can finish writing an email, save it in drafts, continue reading other messages and once the exchange server comes back online, pending works automatically will be done.

Not to mention, an OST file helps recover the lost data from the mailbox, if the Exchange server goes down, crashes or runs into any trouble. OST file’s nature, a carbon copy stored on a hard drive, makes it immune to Exchange Server damages.

Pros and Cons of OST Files


An OST file can be very handy if you encounter a bad connection (limited or unreliable internet).

With the OST file, you can continue your daily tasks of using the mailbox without the need of staying connected with the Exchange Server entirely. Only when sending & receiving an email, the connection is required.

Another advantage of an OST file reveals when the exchange database corrupts and reaches an unrecoverable state. In this predicament, account owners can retrieve data stored on their local computers. Although, this operation might be time-consuming. Plus, to recover the mailbox from an OST, you’ll have to convert it to a PST file first. So, that Outlook can collect data from it, while the original email profile no longer exists.

Also, when your email storage space is full, you can always archive your data in an OST file and save it on your PC.


Unfortunately, an OST file only works for the email profile it belongs to. If the email profile were to be damaged or deleted, the OST becomes useless too. Because without an email profile, fetching data with MS Outlook becomes difficult.

Recovering mailbox data from an OST file requires the extra step of converting an OST file to a PST file which complicates the process somehow. You will need efficient and reliable programs that convert your data flawlessly. For that, today several commercial OST to PST converting software is available in the market.

How to Open an OST File?

Though Outlook automatically creates an OST file, it's not always easy to gain access. To open OST files, proceed as below:

Open Windows Explorer and go to: Drive\User\Username\AppData\Local\Microsoft\Outlook.

When you get disconnected, with Outlook you can automatically access the OST file. If you have several OST files here is how to choose which one to open:

  • Open the Control Panel.
  • Go to "User Accounts".
  • Click on Mail (Microsoft Outlook).
  • Click on the "Email Accounts" button.

Note: you can set one of the OST files as default. So, next time when the internet was cut off, Outlook will use this file automatically.

ms outlook storage location

How to Import an OST File into Outlook?

To import an OST file with Outlook, you can follow the detailed steps below:

    1. At Outlook, select File at the left corner of the top ribbon.
select file in outlook
      1. Click on Open & Export, then Import/Export to start the Import/Export wizard.
click open and export
      1. Then select "Import from another program or file", and click Next.
import the file
      1. After that, select Outlook Data File (.pst) and click Next.
select outlook data file
      1. In the "Import Outlook Data File" Box, use "Browse" to the PST file you intend to import. Also, from Options, choose if you want to replace, create duplicate email data or not, then press Next.
    1. If you were assigned a password to your PST file, enter the password, and press OK.
    1. And if you want to import OST contents into your Microsoft 365 mailbox, choose that mailbox here too. Otherwise, select "Import items into the current folder".
    1. Press Finish to complete the task.

How to Find an OST File?

To find an OST file in Windows, try this process:

    1. Click on the “Data Files” tab and choose the OST file from the list that belongs to the account that you are trying to find.
click on data files
      1. After that, click on the "Open File Location" button.
click open file location button

For Mac users:

All Outlook files on mac, including the OST file are saved in the SQLite database located at: /Users/username/Library/Group Containers/UBF8T346G9. Office/Outlook/Outlook 15 Profiles.

How to Move an OST File Location?

change outlook file destination

If you already have an OST file and intend to move it, plus removing and recreating the account in the profile, proceed as below:

  • Copy the OST file to the new location. If you want to create a new one, you can skip this step.
  • Open File, Account Settings, or open the profile in the Control panel, Mail.
  • Then, delete the account from your profile and click New.
  • Enter your username & password and allow Outlook to find your account information, as we explained above.
  • Press the Change account settings option, and click Next.
  • Click "More Settings".
  • On the "Advanced" tab, press Outlook Data File Settings.
  • Use browses to choose the route to the OST file that you copied at the start, and then click Open. To create a new OST file, use browse to the new location, enter a filename, and then click Open.
  • Then Click Ok to restart Outlook.

How to Convert an OST File?

1. If you have an OST file associated with an Outlook profile

You can create a new PST file for it and copy the items from the open cached mailbox to the new PST. You can read the process below:

  • First, open Outlook, go to the File menu & select the Import/Export option.
  • Choose Export to a file.
  • Select Outlook Data File (.pst) & choose whether to export a specific folder or the whole account.
  • Click Browse to choose where you want to save the PST file and press OK, then click Finish to complete the task.

2. If the OST file is not associated with an Outlook profile with your access

You will need specific software to convert. There are several programs known for converting OST files to PST files. You can also convert your file with the help of free online websites.

How to Recover an OST File?

There are several scenarios in which your OST file data needs to be recovered:

  • When you can't access the Exchange account and there is a corruption issue in an OST file.
  • When your Exchange account is disabled for some reason but still exists.
  • When your Exchange account is deleted.

There are several steps you can take to recover your data, which almost work but do not always completely bring back your lost items. Also, in the worst-case scenario when your account is deleted/disabled from the mail server, you must convert the OST file to PST file format, so that you can restore your emails. In that case, you’ll need the assistance of an OST to PST conversion software such as Wondershare Recoverit.

This User-friendly software is easy to use and quickly recovers your data in three simple steps:

Step 1 Select a location where you lost OST files

Select a hard disk drive where you lost your OST files, click "Start" to scanning lost OST files.

select a hard drive disk

Step 2 Scan the hard disk drive to search lost files

Recoverit will start an all-around scan. Usually, it will take a few minutes to finish the scanning. Sometimes, a few hours are required if many large-sized files are present.

scan computer hard drive disk

Step 3 Preview and recover OST files

After the scan, you can find OST files from "Archive" item on the "File Type". Before you recover, you can preview all the file names contained in the recoverable OST file. Then check and recover them by clicking the "Recover" button.

preview and save photos

Note: To know more about OST file recovery, here’s the guide on ten best Outlook OST recovery softwares.


After learning what is an OST file? Its pros & cons, the instructions in this review will guide you on how to find, open, import, convert, and successfully recover an OST file.


OST stands for "offline storage table" or "Outlook storage table" and is an Outlook data file that is created when the Outlook profile is configured with the MS Exchange server with cached mode enabled.

MS Outlook use this type of file as a replica of the mailbox content on the server that allows users to access the data when disconnected from the server.

Using third-party software is the most valid approach for bringing back your lost OST files. In this case, our recommendation is Wondershare Recoverit data recovery software.