What is OST and PST files in Outlook?

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This article will share important information about different file formats regarding the Outlook email client. This article will be much helpful for individuals or organizations that they use Outlook email client to send and receive email messages as a communication medium.

As a user, when you configure your email account to Outlook, a local copy is stored on your device that helps in accessing the previous synchronized email messages, contacts, tasks, etc., without internet connectivity. A local copy can be in an OST or PST file format, depending on your configuration process.

What is OST file?

This file is created when Cached Exchange Mode is enabled while configuring email accounts in Outlook using IMAP, Outlook.com, Office 365, and Exchange accounts.

Notes: Even after configuration with IMAP account, Outlook makes a PST file to store the email database in the prior Outlook 2010 version.

What is PST file?

PST is another file format that Microsoft Outlook uses to save users’ mailbox data. This data file type is created when users configure their email account in Outlook and choose the POP/SMTP standard type.

OST files become useless when:

Case 1: When you want to share your email information or database with another device, Outlook doesn’t support this task. It is possible only with the help of Free OST viewer tool.

Case 2: If for some reason, your Outlook profile is removed from the Exchange server, you cannot access your stored information in the OST file.

Case 3: Anciently deleted email items cannot be recovered from Exchange Server. You will lose deleted email or Other Outlook items forever.

Case 4:  When you reach the maximum storage limit, your OST file becomes inaccessible. You need to back up in PST format to free up space for new email items.

Case 5: Some unforeseen reasons Exchange Server can be crashed that damage or corrupt Offline data file. So you have to repair OST file for getting previously downloaded items.

PST files become more useful when:

Case 1: If you have stored the email items in PST format, you can easily send it on another device to open and read the PST file in Outlook.

Case 2: When somehow any reason you deleted any email items from the mailbox, you can be recovered easily from Exchange Server.

Case 3: When Outlook profile is deleted or removed by Exchange Server, it doesn’t affect stored Outlook items. 

Case 4: The stored email database in a PST file mailbox does not take space in Exchange Server. So Exchange server work uninterruptedly. 

Case 5: Damaged or corrupted Outlook data file (.pst) can be easily repaired using a third-party OST repair tool or Outlook inbuilt repair tool. 

 Difference between OST and PST files

  • OST file stands for offline storage table and PST file stand for personal storage table.
  • OST file uses .ost extension and PST file uses .pst extension to save email database in a local file.
  • The default location of the OST file is C:\Users\user\AppData\Local\Microsoft\Outlook, and the PST file is stored in Documents\Outlook files.
  • OST files could not be password protected. On the other hand, PST can be protected from passwords, but if someone forget it, they can take the help third-party password removal tool.

Final verdict: After analyzing both Outlook data file formats, we can easily conclude that the OST file has many disadvantages for saving email information compared to the PST file format. So I recommend you to use PST format instead OST file. If you have an OST file, convert OST to PST file format on an urgent basis to avoid undesired circumstances. 

Read more: How to open & import PST file in Outlook?

Read also: How to Convert Microsoft .OST to .PST File in Outlook 2019


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