Offline Outlook Data File: What Is OST File?

Megha Chouhan
Megha Chouhan linkedin | Updated On - December 13, 2022 |

Read time 6 minutes

In the corporate world, a lot is happening around communication, especially through emails. And Outlook is one of the applications that are widely used for email communication. The advantage is that it can be used with Exchange Server and webmails. In Outlook, when you start offline work, a local copy of the mailbox gets stored on the system with all pieces of information like your email messages, calendar, and other items. And to keep all your items, Outlook uses offline Outlook data files, i.e., OST.

Users can access these downloaded or synchronized email messages, calendar information, contacts, and tasks without any email server connection. Users can also compose messages, but they will not be sent; no new messages can be downloaded in the absence of the server too. Similarly, they can add contacts and create appointments. But when the server gets connected, everything will get synchronized. Different accounts(such as Outlook 365 accounts, IMAP accounts, Exchange accounts, and even more)hold the synchronized copy of mailbox information in Offline Outlook Data Files (OST files).

More about OST files

Basically, “OST” stands for an offline Outlook data file or Outlook “Offline Storage Table.” In OST, several types of data, such as calendars, journals, and schedulers, are organized to make data available. In Outlook, OST files are known for keeping data stored offline. Here it creates a local copy in the Cached Exchange Mode or works offline to keep a local copy. When the server is available, the OST file gets synchronized with the server.

The offline folders get automatically updated when the server is available, as those offline folders are replicas of the folders in the server mailbox. Hence after making the server connection, all the offline changes such as adding content, deleting, and any other changes get updated automatically. The whole procedure is known as the synchronization of folders.

How to look for Outlook OST file?
  1. Go to Outlook; select the File tab.Outlook
  2. A window will appear here; select Account Settings; click Account Settings.Account Settings
  3. Now, in the Account Settings window, click the Data Files files
  4. Now, select an .ost file and click Open Folder Location.Open Folder Location
  5. After selecting Open File Location, a window with the file location will appear.file location
Common Errors with the Outlook OST File

While using an Outlook OST file, there would be errors that the user may encounter. We will see some of them here.

  • Orphaned or Corrupt OST file
    When there is no mailbox available on the server, the OST file is called orphaned. And situations like hardware issues, power failure, or the presence of bugs on the system will lead to corrupt OST files. Some error messages related to the OST file are as follows-
  • (0x800CCC0F) Sending / Receiving reported error.
  • Cannot start Microsoft Outlook.
  • (0x8004010F) OST file cannot be accessed.
Methods to Recover Orphaned and Corrupt OST files
Delete OST File and Re-create it

If you cannot access your OST file, then you can opt for this solution. Firstly, you need to delete the OST file by browsing its location. Then Outlook will automatically download the mailbox data from the mail server.

  1. Open Outlook, find the OST file location
  2. Delete the OST file from its location.
Create New Outlook Profile

Before creating a new outlook profile, close the Outlook application. In case you recreate OST file using an existing OST file, always make sure to have a copy of that file in the new location.

  1. Go to Control Panel and click on the Mail option.
  2. A new window will appear; here, go for the Show Profiles option.
  3. Now click the Add option in the appeared window.
  4. Now, a New Profile window will appear; here, type the name and tab on the Next button.
  5. After completing the above procedure, go for the Change Account settings option and click the Next option again.
  6. Select the More Settings option in the Server Settings box.
  7. Click the Advanced option from the above menu and select Outlook Data File Settings.
  8. Next, to save this new OST file, go to the Browse option to change the OST file location. Finally, click on the OK button.
  9. In case you want to use your existing OST file, then browse and select the copied OST file, and click on the Open button.
Use Kernel for OST to PST Converter

Several times, users enquire us that these manual methods are ineffective in resolving the OST problems. We have the option to convert OST to PST format. By understanding the user’s problem, our experts have designed this OST to PST Converter to overcome the complications of manual methods. Effortlessly it recovers all OST items like emails, attachments, contacts, distribution lists, calendars, tasks, and notes and saves them to PST. It also converts OST emails in various other formats such as PST, DBX, MSG, EML, TXT, RTF, HTML, MHTML, & PDF. It works harmoniously with all versions of MS Outlook. OST and PST act like two sides of the same coin. But there are a lot of differences between OST and PST Files.


OST files are extremely helpful when a user wants to access email, appointment calendar, or many more in offline mode without any server connection. But due to OST errors, our work gets disturbed. And manual methods are not always an effective solution. Therefore, to resolve this problem, users can opt to convert OST to PST by using Kernel for OST to PST Converter.

Kernel for OST to PST