BitResQ » What is Outlook.ost File Used For? Complete Guide

What is Outlook.ost File Used For? Complete Guide

What is Outlook.ost File Used For
Shubham Dixit   
Published: Jul 18, 2022 • Tips • 6 Minutes Reading

Summary: If you are concerned about what is Outlook.ost file used for then this article will help you out. Here, you will get all the required information to make you more understand Outlook.ost file. In the end, you’ll know what can you do if something happens with the same file. So, just make sure to read this article till the end to gather all your knowledge.

If you’re also a Microsoft Outlook user, then you must be aware of its related files, i.e PST or OST files.
Although both the files are used for storing data of MS Outlook, the PST file stores data on disk, and the OST file stores the data for offline use.

Now, let’s understand this entire thing in detail.

But, First Know, What is MS Outlook?

Although the Outlook application is an email client which is a part of Microsoft Office. In Outlook, users can not just use it for sending or receiving emails to their clients. But the user can store or manage the calendars, contacts, tasks, etc.
However, Outlook provides multiple configuration methods, using IMAP (Default) or POP.

  • In IMAP Configuration– Using IMAP configuration, you can access your email wherever you are, from any device. That mean, when you read an email message using IMAP, you’re reading it from the email service as it is not downloaded on your computer. So, you can check your email from different devices from anywhere whether it is your phone or a computer.
  • In POP Configuration – On the other hand, the POP works by configuring with your email service and downloading all the new messages from it. In simple words, if you ever want to access any email after downloading them, then you will require the same computer to do so. If you try to access your email from a different device, the previously downloaded emails won’t be available to you. Remember one thing that sent mail is stored locally on your computer, not on the email server.

Although you can use the MS Outlook alone or with an Exchange server, when you sync it with the IMAP server. The OST file is generated.

What is Outlook.ost File Used For?

As of now, you have the idea of what is Outlook, and what is Outlook.ost file. Now, the question arises what type of data this file contains?

So, when you sync the data of any particular email service with Outlook, OST file is generated. However, the email service can be, Gmail, Yahoo, or any. In simple words, it is a synchronization copy of the entire mailbox of an email client in offline mode on a computer. It includes all emails, contacts, calendars, tasks, or other data from the mailbox.

The best thing about Outlook.ost file is you can still access the entire data of the mailbox if the internet connection is interrupted. You can easily compose messages, create appointments, and add as many contacts as you want. But, you will not able to send or download any new email. However, once your internet connection is restored you can do that again, and all the new changes will be synchronized.

What Happens if there is an Error?

Till now, you got the idea that what is Outlook.ost file used for but do you know what happens if there is some error. When the Outlook.ost file cannot be able to connect properly with the Server, then it throws an error every time the user tries to open it.  Such as OST is not an Outlook data file or more. There could be multiple reasons behind hardware crashing, such as –

  • Sometimes, there are virus that affects and harm the Exchange server database and make them unusable . As a result, the .ost file becomes orphaned, the worst thing is when you are unable to open orphaned OST file.
  • Moreover, if there is a force failure occurs, or you shut down the Exchange server inappropriately when the Exchange server is getting to the databases. Then, it becomes the reason that may cause your OST file orphaned. Hence, in this case, you can recreate or rebuild OST file in Outlook again.

How to Open Outlook.ost File on Windows & Mac?

In case, you just want to open OST file without Outlook then you can take the help of the BitResQ Viewer Tool for OST file. This program will let you preview the entire data of all IMAP configured accounts.

For Windows

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For Mac

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Therefore, you just need to download it either on Windows or Mac machine and access the data of the file. The best thing about this automated wizard is free, which means, you should not pay a single penny for it. Hence, it is quite easy to use and read all content of the file along with its attachments.

Solutions when Outlook.ost File is Damage

In case, due to the above-mentioned problems Outlook.ost file gets damaged or corrupted. So, if you are in need to fix the error or repair Outlook.ost file. Then, you can repair corrupted OST file with a professional solution, like BitResQ OST File Recovery Software. It will help you to find out the error existing in the file, and fix them instantly.

Moreover, you will be able to use mentioned software easily on Windows and Mac operating machines irrespective of their versions. Additionally, it is also useful when somehow the OST file size limit increases. So, operate this automated tool without interrupting the Outlook.ost file data.

How to Change Outlook.ost into Outlook .pst?

If you’re having errors continuously in Outlook.ost file, or if you want to use the offline data in the Outlook data file. Because the PST file is more convenient for backup, as you can store them anywhere or easily move them from one to another computer. Therefore, in this case, the BitResQ OST File Converter Tool will be a secure solution for the same. Through this self-oriented program, you can change the Outlook.ost file into PST format and then you can use the file in Outlook again.

While doing this entire procedure your data integrity will be same as earlier. Also, there will be no data loss during and after the changing the file. So, without any uncertainty, you can use this software on either Windows or Mac OS.


Many users out there are still not aware of what is Outlook.ost file used for? So, in this article, we have explained the entire detail about the same. Also, we have provided the solution according to the situation here. So, whatever the case if you can just go with the professional method to read the file. If required then you can fix them as well with no change in data.