A corrupt PST file is one of the few Outlook problems that can lock you out of years of mail in one go. Outlook refuses to open the file, Microsoft’s bundled Inbox Repair Tool either fails or strips out what it cannot parse, and the archive you thought was safe is suddenly a 125 MB brick. Stellar sells two ways out: Stellar Repair for Outlook, an installed Windows application, and Stellar Online PST Repair, a browser service that repairs an uploaded file on Stellar’s servers. I ran the same damaged PST through both. This review covers what each one actually does, what it costs, where it struggles, and which one to reach for.
Disclosure: Stellar supplied the licence key and the sample corrupted PST used for this review, and asked to check the technical details before publication. The testing, comparisons and opinions are our own.
The short version
The desktop application is the better product. It recovered the full folder structure of the sample file, including 17 orphaned items in a Lost & Found folder and three deleted messages it flagged in red, and it let me open every message and attachment before saving anything. The online service repaired the same file for free and produced a downloadable PST, but its preview stops at folder names and item counts, so you are trusting the result until you open it in Outlook. Buy the desktop version for anything you care about or anything over 500 MB. Use the online service when the file is small, the mailbox is not sensitive, and you want it fixed in the next fifteen minutes without installing anything.
Before you run either tool
Copy the damaged PST somewhere safe and work on the copy. Every repair tool, including Stellar’s, writes a new file rather than patching the original, but a second copy costs nothing and protects you from your own mistakes. Then try SCANPST.EXE, Microsoft’s free Inbox Repair Tool, which ships with every Outlook installation. It handles minor header damage well and costs nothing. Microsoft’s own guidance is candid that some items may not be recoverable, and when testing, SCANPST failed outright on a 1 GB file that Stellar repaired in six minutes. If SCANPST reports errors it cannot fix, or Outlook still will not open the file afterwards, that is when a commercial tool earns its price.
Stellar Repair for Outlook: the desktop application
The current release is version 14.0.0.1. It is a 64-bit Windows application that runs on Windows 8 through Windows 11, needs 8 GB of RAM (Stellar recommends 16 GB and 64-bit Outlook for large files), and about 250 MB of disk space. One requirement catches people out: you need a licensed copy of Outlook installed on the same machine to save the repaired data as a PST. The application scans and previews without Outlook, but the final export uses Outlook’s own libraries to write the file. Stellar’s system requirements page lists Outlook 2007 through Outlook 2024 and Microsoft 365 as supported.
Installation and activation
Installation is a standard wizard: language, licence agreement, install location, shortcuts, done. Activation is a menu item on the ribbon where you paste the licence key. The unactivated build works as a demo: it scans and previews everything, but the Save Repaired File button will not export until you activate. That is a fair trial model, because you can see exactly what will be recovered before paying, though it does mean the trial cannot get your mail back on its own.
Repairing the sample file
The Select Outlook Data File dialog opens automatically and offers two tabs. Profile List reads the PST paths from your configured Outlook profiles, which is convenient if the broken file is the one Outlook is currently complaining about. Choose Mailbox Manually lets you browse to any PST, and a Find button searches a drive for PST files when you do not know where the archive lives. I used manual selection to point it at the 125 MB sample, then clicked Repair.
There is no scan-mode choice. You select the file, click Repair, and it scans. The 125 MB sample is a small file by PST standards, and the scan finished in less than a minute. That matches other published tests: TechSpective timed a 124 MB file at 59 seconds and a 1 GB file at six minutes on an i7 with 16 GB of RAM, and GBHackers reported about 12 minutes for a 4.37 GB file and roughly 40 minutes for a heavily corrupted 25 GB archive on an i5-12400. Expect the scan to scale with file size and damage, and expect it to lean on the CPU while it runs. Capterra reviewers repeatedly mention high resource use on very large files, which is consistent with those numbers.
What the preview showed
After the scan, the application switches to a three-pane layout that will feel familiar to anyone who has used Outlook: folder tree on the left, message list in the middle, reading pane on the right. For the sample file, it rebuilt the standard Outlook folder set with item counts: 60 mail items in total, of which 56 sat in the Inbox and 2 in Deleted Items, plus 2 calendar entries, 1 contact, 7 journal entries and 6 notes. It also created a Lost & Found folder holding 17 items whose parent folder could not be determined. That folder is the real test of a repair tool. A weak repair silently drops orphaned items; Stellar keeps them and lets you decide.
Three messages in the Inbox were listed in red with a bin icon beside them. Those are items the sender had deleted but which still existed in the file’s data structures, and Stellar recovers them alongside everything else. Attachments show a paperclip in the list and open from the reading pane. Search boxes sit above the From, To, and Subject columns, and a separate Find Message button on the ribbon runs a more detailed search across the whole file. The bottom-left icons switch between Mail, Calendar, Contacts and the other item types, so you can check that the calendar entries and contacts came through rather than judging the whole recovery from the mail folders. The sample mailbox is obviously synthetic test data (subjects like “testing” and “reward”), so I cannot say anything about fidelity on real HTML-heavy corporate mail, but subjects, senders, item types, and attachment names all rendered correctly in the preview.
Saving and the other features
Save Repaired File opens a dialog where you pick the format and destination. The Professional edition writes PST, MSG, EML, RTF, HTML and PDF. Saving as PST is the normal choice, and you then open the new file in Outlook. Stellar advises closing Outlook while the export runs. An Apply Filter option narrows what gets saved, including whether recovered deleted items are included, and you can untick folders in the tree to save only what you need. Right-clicking a single message offers a quick save in any of the formats, which is handy when you only need one contract or one thread out of a broken archive. Two features matter more on big files than on my sample: Save Scan writes the scan results to disk so you can come back later without rescanning, and the exporter automatically splits output PSTs at roughly 45 GB. The application also repairs encrypted PSTs and accepts source files from Outlook 2007 through 2024, both ANSI and Unicode.
Editions and pricing
Stellar sells three editions, each licensed for one machine. Prices below are the one-year licence prices shown on Stellar’s site at the time of writing; lifetime licences are offered at checkout for more, and every edition carries a 30-day money-back guarantee.
| Edition | Price (1 year) | What you get |
|---|---|---|
| Professional | $79 | PST repair, deleted-item recovery, preview, filters, save to PST, MSG, EML, RTF, HTML and PDF |
| Technician | $149 | Everything in Professional plus export to Microsoft 365 and live Exchange, MBOX output, and PST split and compact tools |
| Toolkit | $199 | Everything in Technician plus six more utilities: Converter for OST, Splitter, Compactor, Merge Mailbox, Password Recovery and Undelete Email |
Two things to note before buying. Microsoft 365 and Exchange export are Technician features, so a Professional licence will not push a repaired mailbox straight into a cloud tenant. And the one-year term is the headline price; if you expect to repair files more than once, the lifetime option is cheaper over time. The gap between Technician and Toolkit is only $50, and Toolkit’s OST converter alone is worth that if you also deal with orphaned Exchange caches.
Stellar Online PST Repair: the browser service
The online service is a four-step web page: sign in, upload, repair, download. It requires an account but no card for the free tier. The Free plan repairs one PST of up to 500 MB and keeps the repaired file on Stellar’s servers for 24 hours. Premium costs $29.99 per file, raises the limit to 5 GB and keeps the result for 48 hours. It handles one file per job, supports ANSI and Unicode PSTs from Outlook 2003 through 2024, and accepts password-protected files. Stellar’s FAQ says most repairs complete within 15 minutes, with larger or more damaged files taking longer.
I uploaded the same 125 MB sample on the free plan. The upload is the slow part on a home connection. Once the repair finished, the page reported “File Repaired Successfully” and offered two options: Preview and Save PST File.
The preview is the weak point. It generates an HTML report of the recovered folder structure and item counts. You can see which folders came back and how many items each holds, but you cannot open a message, view an attachment, or search for a subject line before downloading. For a mailbox where you need to confirm one specific email survived, that is not enough; you download the PST, open it in Outlook, and find out then. The desktop application’s item-level preview is the single biggest reason to prefer it.
Then there is the privacy question. Uploading a mailbox to a third-party server is a decision, not a click. Stellar states that the transfer is encrypted, that repairs run with no human touchpoint, and that files are permanently deleted after the retention window. Those are the vendor’s statements, and I have no way to audit them. For a personal archive, that is probably fine. For a work mailbox containing client data, a company’s data-handling policy or a regulator may forbid it regardless of what the vendor promises, and the desktop tool keeps everything on your machine.
Time also matters more than the 15-minute figure suggests. A 1 GB PST on a 20 Mbps upload takes about seven minutes to transfer before the repair even starts, and you then download a file of similar size. On a slow or metered connection, the desktop application will finish first.
Desktop versus online
| Desktop (Professional) | Online | |
|---|---|---|
| Where the file is processed | Your PC | Stellar’s servers |
| File size | No stated limit | 500 MB free, 5 GB Premium |
| Preview before saving | Every message, attachment, contact and calendar item | Folder names and item counts only |
| Deleted-item recovery | Yes, highlighted in red | Not shown in the preview |
| Output formats | PST, MSG, EML, RTF, HTML, PDF | PST |
| Microsoft 365 / Exchange export | Technician edition | No |
| Outlook required | Yes, to save | No, but you need it to open the result |
| Cost | $79 per year, one machine | Free under 500 MB, $29.99 per file up to 5 GB |
| Repeat use | Unlimited files during the licence | Pay per file above 500 MB |
Which one should you use?
Choose the desktop application when the file is over 500 MB, when the mailbox contains anything you would not email to a stranger, when you need to confirm specific items survived before you commit, when you want individual messages out in EML, MSG or PDF, or when you are an IT technician who will do this again. Two Premium online jobs cost more than half a Professional licence, and the licence covers unlimited files for a year.
Choose the online service when the file is under 500 MB, the content is not sensitive, you do not have Outlook on the machine in front of you, and you want a repaired file in the next quarter of an hour without installing software. Under those conditions, it is free, and the result was a valid PST.
Severity of corruption is not a reason to pick one over the other. Neither product page claims a stronger repair for one over the other. The differences are about size, privacy, inspection, and cost.
Pros and cons
Stellar Repair for Outlook (desktop)
- Pro: Rebuilt the full folder structure, kept 17 orphaned items in Lost & Found and recovered three deleted messages on the sample file.
- Pro: Item-level preview lets you verify everything before paying or saving.
- Pro: Six output formats, per-message quick save, filters, saved scans and automatic splitting of large output files.
- Pro: No file size limit, and independent tests show it scaling to 25 GB archives.
- Pro: Clean install with no bundled extras, and a 30-day money-back guarantee.
- Con: Needs a licensed Outlook on the same machine to save a PST.
- Con: Windows only, and 64-bit only.
- Con: $79 per year for one machine is steep for a one-off repair, and Microsoft 365 or Exchange export needs the $149 Technician edition.
- Con: Heavy CPU and memory use on multi-gigabyte files, according to several user reviews.
Stellar Online PST Repair
- Pro: Free for files up to 500 MB, with no card required.
- Pro: Nothing to install, and it works from any machine with a browser.
- Pro: Repaired the 125 MB sample on the free plan and offered the result as a downloadable PST.
- Con: Preview shows folders and counts only, not messages.
- Con: Your mailbox leaves your machine; data-handling promises are the vendor’s word.
- Con: Hard 5 GB ceiling, one file per job, and $29.99 per file above 500 MB adds up fast.
- Con: Upload and download time on slower connections can exceed the repair itself.
- Con: The repaired file expires after 24 or 48 hours, so download it promptly.
Verdict
Stellar Repair for Outlook does the job it is sold for. On the sample file, it recovered everything, including deleted and orphaned items, and showed me all of it before asking for money. The price and the Outlook dependency are real drawbacks, but the trial removes the guesswork: scan first, and only pay if the preview shows the mail you need. The online service is a genuinely useful free tool for small, non-sensitive files, and a reasonable $29.99 emergency fix for a single larger one, but its thin preview and the upload requirement make it the second choice for anything important. If you have one broken PST and it is under 500 MB, start online for nothing. If it is bigger, or it matters, buy the desktop application.
