Purpose of Files with the .ost File Extension

The .ost File Extension ? An Explanation

The .ost file type is associated with Outlook, a popular e-mail program from Microsoft. The term OST is an acronym for Offline Storage Files. .ost files are offline files that are used by Outlook. Although they are similar to .pst (Personal Folder) files, they have greater storage capacity than .pst files which have a 2GB size limit.

Operating System

Outlook and .ost files work only on Windows computers.

Purpose of .ost files

.ost files store e-mails as you receive them from your mail server. As the .ost files are stored on your local hard drive, instead of on the mail server, these files allow users to read received e-mail messages even when the connection with the mail server is lost. When the connection with the mail server is restored, Outlook synchronizes the e-mail account files and the .ost files.

Another important use of .ost files is that they allow e-mail messages to be recovered if the e-mail server crashes.

How to recover data from .ost files

  1. Open Microsoft Outlook.
  2. Click the Tools menu and then select Email Accounts.
  3. Select the View or Change Existing E-mail Accounts option and click the Next button.
  4. Select the Exchange Server.
  5. Click Change.
  6. Click More Settings.
  7. Click the Manually Control Connection State option to have Outlook start offline the next time you open Outlook.
  8. Click Work Offline and Use Dial-up Networking to prevent Outlook from connecting with the e-mail server when it re-opens.
  9. Close Outlook.
  10. Re-open Outlook.
  11. Select the Work Offline option.
  12. Click the Tools menu and select Services to open its corresponding dialog box.
  13. Click the Services tab and then click Add.
  14. Select Personal Folders.
  15. Click the OK button.
  16. Enter the name of the folder and specify its location (for e.g. desktop) and then click OK.
  17. Drag the Personal Folder from the Outlook Window to the new folder (this moves the .ost files to the personal folder).

Now, when your Windows computer syncs with the e-mail server, .ost files can be copied to recreate your e-mail messages.

How to convert .ost files to the .pst file format

To convert .ost files to the .pst file format, you require software, such as Outlook Recovery Toolbox.

Names of the programs that can open .ost files in Windows

  • Microsoft Outlook
  • Outlook Recovery Toolbox
  • Microsoft Outlook OST Integrity Tool

In case you are unable to open an .ost file using Outlook, try opening the file with a reliable file repair program.