OST is simply a cache file that allows you to access your Outlook profile offline. If the OST file becomes corrupted for any of a variety of reasons, you can delete it from the local folder and recreate it from the server. However, if the user profile has been deleted from the network server and the mailbox backup has been lost, users can recover their mailbox data in the PST file format by using the locally saved OST file. You can easily import that PST file into your new Outlook profile. Unfortunately, there are no free tools or PowerShell commands for converting the encrypted orphaned OST files. You will need to use third-party tools for this work. Recommended BLR OST converter tool available in the market.
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Import Corrupted OST files into PST - With BLR OST Converter
Re: Import Corrupted OST files into PST - With BLR OST Converter
To easily convert OST to PST file format with all emails, contacts, calendars, etc. using CubexSoft OST to PST Converter Tool. This software allows you to bulk export OST file to PST file format without Outlook. It has a very simple GUI, everyone can easily handle and manage the software without any help. There is no need to install the MS Outlook email program for the conversion process. During the process, the software keeps all the folder structures without any changes or data loss. It was compatible with both Mac OS and Windows OS.