26 Aug

Since the advent of Office 365, many users’ needs to switch from other emailing services like Gmail, thunderbirds, windows live mail, google apps, MS Exchange servers, etc. However, for different types of migrations, there are other methods available. Besides this, migration is also needed when the data file becomes inaccessible, and you need to open it in Office 365.

 Let me briefly explain the OST file. It is a cached copy of the MS exchange server mailbox. When MS Outlook is configured with an Exchange server, an OST file is created on the users' machine to store the cached data for its availability in offline mode. This OST file let you access and view your mailbox anytime and anywhere, irrespective of the internet connection. But, many a time, this OST file becomes inaccessible for various reasons.


When an OST file becomes inaccessible, a lot of problems may arise.

  1. You cannot view or access the Outlook emails.
  2. When you open Outlook, it will show you an OST file error message.
  3. You may lose your complete data permanently if the server connectivity is not restabilized soon.
  4. The new emails cannot be sent or received by the users if the OST file becomes inaccessible.
  5. Loss of time, effort, and productivity
  6. You won’t be able to open it in MS Office 365

 To stay away from all these problems, one might not let their OST file get corrupt or infected by any means. Still, there is a high possibility of this happening to you.

How to Open an Inaccessible OST file in Office 365? 

One of the causes of OST file inaccessibility is MS Exchange server failure. Besides this, OST file corruption can also make it inaccessible. In both situations, you won’t be able to open the file in Office 365. However, you can solve this problem, if you somehow convert OST to PST file format.

PST file is another type of Outlook data file that MS Outlook creates when you configure it locally with an IMAP account. It is easy to open or import PST files into any MS Outlook account, including Outlook for Office 365. But before we understand how to import OST in Office 365, let us know if it is possible to convert OST into PST directly? 

How to Convert Inaccessible OST into PST File Format? 

It is a cumbersome task to directly export an inaccessible OST into PST format. Since inaccessible OST files are usually corrupt, no application will be able to read the file. However, if you know the server to which this OST file belongs, then you can restore the data file from scratch. 

Besides this, you need to opt for a reliable OST to PST converter which can do the job in seconds. These tools are designed with intelligence to read the corrupt or inaccessible orphan OST files and export them to PST file format. Nowadays, these tools provide multiple options to convert OST to MBOX as well as EML, MSG, or HTML to use the OST file data into any desirable application accepting Outlook.

How to Open Inaccessible OST file in Office 365?

You can use any of the above methods to save OST into PST file format. You can import this PST file into SM Outlook for office 365 by using one of the following methods: 

  1. Use Azure AZ copy: It is advisable for those, who are technically strong to understand the steps. It is a manual process to import PST into Outlook 365.
  2. Drive shipping: In this, you need to send a hard copy of the PST file to the Microsoft team. They will upload the files on your behalf. This method is suitable if you have a large amount of data to export.
  3. Import/Export Wizard: opt for this method if you have a handful of PST files to export into Office 365. You need to; open Outlook >> File >> Import / Export >> Select the file to import >> Browse the PST file, and you are done.

Microsoft offers almost everything that makes your job easy. Still, there are certain things that Microsoft does not provide. That is why we are explaining here; how to bridge the gap between OST and PST file formats.