Stellar Converter for OST – Review, Test-Drive and Benchmarks A review and test-drive of Stellar Converter for OST, a useful software to convert inaccessible OST files into MS Outlook PST files

Stellar Converter for OST - Review, Test-Drive and Benchmarks

In this post we’ll take an extensive look at Stellar Converter for OST, a powerful recovery software that can be used to convert inaccessible OST files into accessible Outlook PST files.

Truth to be told, it’s not the first time we’re talking about it: we already mentioned Stellar Utilities, and more precisely their MS Exchange EDB Recovery Tool, in this post. In this article we’re going to talk about MS Outlook, which is currently the #4 most used e-mail client:

Stellar Converter for OST - Review, Test-Drive and Benchmarks
Source:, November 2019

OST and PST, aka MS Outlook data files

When you add an e-mail account to Outlook, a local copy of all the e-mail message you download is stored on your computer: this feature allows you to access your previously downloaded or synchronized email messages, calendar information, contacts, and tasks without an internet connection.

Now, certain types of accounts, such as POP accounts, store their information in Outlook Data Files, which are stored on the filesystem with the .pst extension: those are the PST files. Other types of accounts, such as Outlook 365 accounts, Exchange accounts, IMAP accounts, and accounts store their information in Offline Outlook Data Files, which are stored with the .ost file extension: those are the OST files.

Let’s now briefly review the most relevant differences between these two formats.

Outlook Data File (PST)

An Outlook Data File (PST) contains your messages and other Outlook items and is saved on your computer.

NOTE: In Outlook 2013 and earlier versions, IMAP accounts also used an Outlook Data File (.pst); since Outlook 2016 and Outlook for Office 365, IMAP accounts have been switched to use Offline Outlook Data Files (.ost) format instead.

Outlook Data Files can also be used to backup or export items from any type of email account, or to import email messages, calendar, contact, and task data from another Outlook Data File. Because these files are saved on our computer, they aren’t subject to mailbox size limits on a mail server; this means that, by moving items to an Outlook Data File (.pst) on our computer, we can free up storage space in the mailbox on our mail server. However, this also means that those items will only be available on the computer where the file is saved.

Offline Outlook Data File (OST)

Most other account types, such as IMAP accounts, Office 365 accounts, Exchange accounts, and accounts use an Offline Outlook Data File (OST) file to store a synchronized copy of our mailbox information on our local computer. When our connection to the mail server is interrupted, for example, when we’re on an airplane without WiFi or if your internet connection disconnects, we can still access all emails, calendar data, contacts, and tasks that have been previously downloaded.

This means that we can read and compose messages, create appointments, and add contacts: however, if we’re offline, our email messages won’t be sent and no new messages will be downloaded until our internet connection is restored. When the connection is restored, changes are automatically synchronized, and the folders and items on the server and on our computer will be identical again in a matter of seconds (or so, depending on our connection speed).

Stellar Converter for OST

Stellar Converter for OST is a conversion tool able to convert all OST mailbox items – emails, attachments, contacts, calendars & deleted items – and extracts them as PST while retaining their overall structure. The resulting PST file will be an exact replica of the mailbox data that user would have access to in normal conditions when her OST could be synchronized with Exchange.

The conversion speed is also relatively fast: from our tests with an average i3 desktop machine, the software took approximately 40 minutes to convert a 5GB OST into a PST (8 minutes per GB). Such performances arguably make this tool the fastest converter available on the market nowadays, at least according to these official benchmarks.

Its main features include:

  • Search and save individual emails within the same OST file
  • Converts encrypted OST files into PST files. Also works on IMAP OST files
  • Converts large OST files to PST – No file size limitation
  • Free OST to PST conversion for first 20 emails per folder
  • Easily exports OST file to Office 365 & Live Exchange (Tech version only)
  • Converts multiple OST files to PST format (Tech version only)

Common usage scenarios

Being able to convert our e-mail data from OST to PST files is not a everyday task by any means, but it can be very important in some specific scenarios, such as the following ones.

Stellar Converter for OST - Review, Test-Drive and Benchmarks
Stellar Converter for OST – initial screen

Inaccessible or Orphaned OST File

It’s common for IT administrators to come across situations like Exchange Server crash or mailbox synchronization problems which make OST file inaccessible or orphan. Likewise, a user’s desktop may fail to boot due to hardware problem or malware infection, or the storage drive containing OST file may have large number of bad sectors. The outcome of these situations is an inaccessible OST, with risk of losing mailbox data such as emails, attachments, contacts, etc. Stellar Converter for OST converts inaccessible OST file & extracts mailbox data in PST file.

Migration to New Email Service

When you migrate to a new email service or platform, it’s a challenge to gain access to the mailbox data stored in OST files of user accounts configured with older email service. This becomes a critical situation when there’s no PST backup of these OST files. In this case, you would lose the mailbox data stored in such OST files unless you convert the OST to an accessible format like PST. Our OST to PST converter software converts inaccessible OST file and extracts complete mailbox data – emails, attachments, contacts, notes, etc. – in PST format.

Migration to a New Computer

The OST file is local cache of the user’s Exchange mailbox, which can’t be directly imported in Outlook or opened on any another system. So when you change over to a new computer, the data stored in the OST will be lost unless you find a way to extract the OST data in a format like PST which can then be opened in Outlook client installed on the new machine or anywhere else. The OST PST conversion tool serves as a powerful software to convert OST file and extract the mailbox data in PST format. The software ensures that complete mailbox data is extracted

Difficulties with Using Outlook Import/Export Wizard

Outlook built-in Import/Export Wizard is an amazing utility for migrating OST data to PST format. But the tool requires users to have considerable technical proficiency and spend time to get the expected results. It also needs the same original Exchange account for this task, and you cannot convert inaccessible OST files with the help of Import/Export Wizard. Stellar Converter for OST software provides an easy and fast way to convert the OST file into PST via a rich Graphical User Interface. The OST PST conversion tool extracts OST data with 100% precision and original integrity.

Basic Features Breakdown

Here’s a detailed features breakdown for all versions of the Stellar Converter for OST tool:

Extracts Mailbox Items from Inaccessible OST to PST

There could be several situations when you may need to export the data from OST file to PST format. These could include inaccessible OST file, organization migrating to another email platform, user changing over to a new system, and more. OST PST converter quickly extracts mailbox data from inaccessible OST file and saves it in a fresh PST which can be imported in Outlook to restore mailbox access. It extracts all mailbox items including emails, attachments, contacts, calendars & deleted items. See steps to convert OST file into PST using Stellar Converter for OST.

Extracts Exchange Objects from OST with High Precision

The OST PST Converter Software extracts all Exchange mailbox objects such as emails, contacts, attachments, notes, journals, calendar entries, etc. from OST files and saves them in PST format. The tool performs 100% precise OST 2 PST conversion, and maintains original integrity of mailbox items. Its advanced scan engine parses OST files of any size (no file size limitation) and extracts complete mailbox data including emails, attachments, contacts, and calendars. The software offers administrators most precise OST conversion at speed, So, it offers administrators the best of precision & speed, thereby freeing up their valuable time & efforts for more strategic projects.

Stellar Converter for OST - Review, Test-Drive and Benchmarks
After being performed, OST scans can be saved and then retrieved for later use

Converts OST Data in Multiple File Formats

The Powerful OST to PST Converter Software also provides the option to search and save individual email messages from within OST files. In case you do not have time or do not wish to convert all OST items to PST, you can choose specific email messages to be extracted from the OST based on various parameters such as ‘To’, ‘From’, ‘Subject’, and ‘Date’ and convert them into a variety of formats including MSG, EML, RTF, HTML, and PDF formats. This feature lends this tool a high degree of flexibility, making it stand above its competition.

Organizes Mailbox Messages to Improve Readability

The OST PST Converter Software extracts mailbox data in an organized manner while maintaining the original format and arrangement of items. Once OST scanning is completed and all recoverable items have been discovered, the product allows you to sort and organize your email messages by Date, From, To, Subject, Type, Attachment, Importance, etc. Additionally, it lets you improve scan result readability by allowing you to segregate emails in groups by using a convenient “Show in Groups” feature.

Outlook-Like GUI for Seamless OST Conversion

The software is equipped with a familiar Outlook-like GUI that makes working with it a breeze. Helpful instructions and proper labeling of tasks and buttons at every step simplify & enrich the experience for all users. Smart preview of objects before conversion, choice to save converted data at any desired location on the system or network, multiple formats to save individual mail messages, etc. make OST to PST Converter software one of the best tools in its category.

Conversion of Encrypted OST file

Users encrypt OST file to keep their important information secure from unauthorized access. Sometimes you may experience an error that it is not an Outlook Data file when trying to open encrypted OST file. In such situation, you may lose access to the data stored on your encrypted OST file. To overcome such issues, you would need to convert the encrypted OST file to PST format. OST converter tool converts encrypted OST file to PST and regain access of mailbox data.

Free OST to PST Converter

The converter tool allows free OST file to PST file Conversion for 20 emails per folder. All you need to do is download the Free version of the software and scan your OST Files. After scanning, the software shows the preview of converted OST file & supports free conversion for only OST to PST file format. To save free 20 emails per folder, just click on ‘Save converted file’ button & the converted OST file will be saved at your specified location.

Wide Compatibility with Microsoft Office

One of the highlights of this tool is its compatibility with a number of MS Office versions. It supports MS Office 2019, 2016, 2013 (32 bit version and 64 bit versions), MS Office 2010 (32 bit and 64 bit versions) / 2007 / 2003 / 2002 (XP) / 2000.

OST Conversion at Your Pace & Convenience

The software allows to save the scanned information as a DAT file which can be loaded anytime later to reinstate OST to PST conversion process. Through this feature, users can split the scan and preview instances in the process, and save the mailbox in PST without the need to repeat the scanning process.  This is particularly used when a user is too busy to carry out the whole operation at one-go; furthermore, DAT file ensures that time is not wasted in repeat scanning of the same data.

Technician Edition Features Breakdown

These advanced features are only available in the Stellar Converter for OST – Technician Edition and are specifically designed for System Administrators that frequently work with OST files.

Batch conversion Module

Batch Conversion procedure involves selection of multiple OST files and their subsequent conversion into PST files through a single process. This option to save the corresponding PST at the same location helps in tracing the PST files with ease. An option to save PST file at preferred (user-specified) location is also available. All OST files can be directly converted into PST files or it can be done by splitting the PST files on the basis of either “Split by Date” or “Split by Size” option.

Exports Mailbox Data from OST to Office 365

Migration to Office 365 is easier with this software as it can directly export the OST to PST converted files to Office 365. All you need to have is Office 365 account with valid login credentials. This software relieves you from the lengthy and time-taking mailbox migration procedure.

Splits and Compacts Large PST Files

The Software provides two advanced options for newly created PST file: Split & Compact. To compress the converted PST file, you just need to click on “Compact & Save PST” option, and it decreases the size of PST file in the disk. The ‘Split’ feature is helpful if you have a bigger PST file and you want to split it into smaller PSTs to reduce the possibilities of PST file corruption.

Software Download

Stellar Converter for OST can be downloaded from the official site at the following URLs:

The Basic Edition Free Download enables you to preview the converted file and save 20 items per folder; the Technician Edition Free Demo allows you to check preview all the mail items & save 20 items per folder.

Other Downloads

About Stellar Data Recovery

Stellar Data Recovery (formerly Stellar Phoenix, now simply known as Stellar) is a leading data care corporation based in India, with presence in the US and Europe. It’s a ISO 9001 & ISO 27001 certified organization specializes in Data Recovery, Data Erasure, Mailbox Conversion, and File Repair software and services.

Over the past 25 years, the company has consistently organized their resources and efforts around developing innovative, future-ready solutions that are unrivalled on capability and built with the core purpose of enabling comprehensive data care for users in the consumers and enterprise segments.


We tested Stellar Data Recovery for OST against a single MS Outlook OST file containing roughly 5GB of e-mail messages from a MS Exchange Online account and it successfully performed the task of converting them out to PST in less than 40 minutes with flawless results: all in all we were very happy of what we’ve seen and can’t but recommend it to anyone – from MS Outlook users to System Administrators – who needs to perform these kind of conversions.


About Alice

Layout designer, SEO & marketing analyst. Since 2010 is also a junior developer, working on the web site back-end infrastructure of some italian press companies. She also actively manages a number of social pages (Facebook, Twitter, LinkedIn) for some IT companies and press agencies.

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