Converting Inaccessible OST Files to PST Using Stellar Converter – Product Review
Anyone who manages Microsoft Exchange or Microsoft 365 long enough will eventually face the same situation: a user has left the organization, the mailbox has been deleted, and someone still needs access to the data. At that point, native Microsoft tools are often no longer useful, and all you are left with is an Outlook OST file.
In this review, I tested Stellar Converter for OST in a realistic lab environment to see how it performs in exactly these scenarios. The goal was not to read feature lists, but to see how this OST to PST Converter behaves when used the way administrators actually use it.
What Stellar Converter for OST Is Designed to Do?
Stellar Converter for OST is designed to extract mailbox data from Outlook OST files and convert it into usable formats such as PST, or export it directly to Microsoft 365 or Exchange Server, even when the original mailbox is no longer available.
Typical use cases include:
- Deleted or disabled Microsoft 365 mailboxes
- Orphaned OST files after Outlook profile removal
- Corrupted or inaccessible OST files
- Legal, audit, and compliance recovery scenarios
Lab Environment and Test Setup
To keep the review realistic, I created a small but practical lab environment similar to what I encounter in enterprise support cases.
Exchange / Mailbox Context
- Cached Exchange Mode enabled
- OST file generated locally
- Mailbox later deleted from Exchange Server
- Outlook profile removed, leaving the OST orphaned
This setup mirrors a very common off-boarding or compliance request scenario.
Installation Experience
Installation was straightforward and completed in under two minutes.
- No additional prerequisites
- No background services installed
- Clean and simple installer
Once installed, the application opens directly to the OST selection screen, which is exactly what you want in a recovery tool.
Scanning the OST Files
After selecting the OST file, I started the scan and monitored system behavior closely.
Observations During Scan
- Scans completed successfully on all file sizes
- No crashes or application hangs
- UI remained responsive throughout
- CPU and memory usage stayed within reasonable limits
Mailbox Preview and Data Validation
Once the scan completed, Stellar Converter for OST presented a full mailbox tree.
I manually verified:
- Folder hierarchy and subfolders
- Email headers and body content
- Attachments (opened correctly)
- Calendar appointments
- Contacts
- Unicode and non-English characters
The converted data looked consistent with what I would expect from a live mailbox.
Export and Conversion Testing
Export to PST
I exported the mailbox to PST and opened it in:
- Outlook 2019
- Outlook (Microsoft 365 Apps)
The PST opened without errors, folder structure was intact, and large mailboxes were handled correctly.
Export to Microsoft 365
I also tested direct export to Microsoft 365.
- Admin credentials were used
- Mailbox import completed successfully
- No duplicate folders or items observed
- Data appeared correctly in the destination mailbox
Selective Export
Date-range filtering and folder-level export were also tested. These options are particularly useful for compliance or legal requests where only specific data sets are required.
Performance and Stability
Across repeated scans and exports:
- No unexpected crashes
- Predictable scan and export times
- System remained usable during operations
From an admin perspective, this predictable behaviour is critical when working under time pressure.
Security and Compliance Perspective
From what I observed:
- All processing is done locally
- OST files are accessed in read-only mode
- No forced cloud connectivity
- Suitable for audit and forensic workflows
This aligns well with enterprise security expectations.
Limitations Observed
It’s important to be realistic about the limitations:
- Export requires a paid license (expected)
Overall Rating and Verdict
Final Rating: ⭐ 4.6 / 5
Stellar Converter for OST performs reliably in the scenarios where Exchange administrators actually need it when the mailbox is gone and the OST file is the only remaining source of data. The tool is stable, handles large OST files well, and provides practical export options for Microsoft 365 and PST. From a sysadmin and Exchange administrator perspective, Stellar Converter for OST earns a solid 4.6 out of 5 and is a dependable conversion utility for emergency conversion scenarios.
