Restore unreadable, damaged, or oversized Microsoft Outlook databases (.pst and .ost) using two recovery workflows powered by the exact same closed binary reconstruction algorithm: fix your file online in any browser, or run 100% local offline recovery on a Windows PC with PST Repair Kit. Both options include a built-in Free PST Viewer that lets you browse recovered folders, read emails, and check attachments and contacts for free before paying - even if Microsoft Outlook is not installed on your device.
Online PST & OST Repair in Browser ($10 per 1 GB): Upload a damaged .pst or .ost file from any smartphone, tablet, Mac, or Windows PC without installing Microsoft Outlook. Inspect your restored mailbox on the free preview page and download a free DEMO recovery file before paying.
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Download PST Repair Kit for Windows PC
PST Repair Kit for Windows (License from $39): Install on Windows for 100% local offline processing where confidential data never leaves your computer. View all recovered items for free, export up to 5 recovered objects per folder in demo mode, and unlock unlimited file sizes and batch repairs with a license.
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Because both our web application on https://www.outlookpst.repair/ and the desktop PST Repair Kit for Windows run the identical proprietary recovery engine, restoration depth and folder structure accuracy are exactly the same. Select the workflow that matches your device, file size, and privacy policy:
| Selection Criterion | Online Recovery Service | PST Repair Kit (Windows) |
|---|---|---|
| Supported Devices | Phones, tablets, Mac, PC | Windows 11, 10, 8.1, 8, 7, Server |
| Recovery Engine | Closed B-tree algorithm | Identical B-tree algorithm |
| Input File Types | Corrupted .PST and .OST | Corrupted .PST databases |
| Data Privacy | Encrypted cloud processing | 100% local (zero data egress) |
| Outlook Required? | No (100% standalone) | No for Free PST Viewer mode |
| Free Pre-Check | Web preview + DEMO file | Local preview + 5 items/folder |
| File Size & Count | Ideal up to 3–4 GB | Unlimited size & file count |
| Pricing Model | $10 per 1 GB of source file | From $39 (unlimited files) |
Strict Local Privacy (Zero Data Egress): For legal, medical, financial, or corporate mailboxes governed by strict NDA or GDPR rules, PST Repair Kit executes every read/write operation locally on your computer's CPU and disk without transmitting a single byte outside your machine.
When your main database is damaged, Microsoft Outlook usually freezes on startup, blocking access to its internal Account Settings > Data Files menu. Use the direct Windows paths below to locate your file in 30 seconds and avoid three common actions that permanently destroy surviving data clusters.
Press Win + R on your keyboard (or click the address bar in Windows File Explorer), paste the path below, and press Enter:
%userprofile%\Documents\Outlook Files to locate standard personal storage tables.%localappdata%\Microsoft\Outlook to open the hidden C:\Users\<YourUsername>\AppData\Local\Microsoft\Outlook directory where Exchange, Microsoft 365, and modern IMAP .ost files are stored.C:\Windows.old\Users\<YourUsername>\AppData\Local\Microsoft\Outlook and C:\Windows.old\Users\<YourUsername>\Documents\Outlook Files.outlook(1).pst or user(1).ost—weighing only 265 KB to 15 MB. Sort your folder by the Size column and select the large original file (hundreds of megabytes or multiple gigabytes) modified prior to the crash.
C:\OutlookRecovery) before starting, keeping the original file untouched as a backup.OUTLOOK.EXE process running or selecting an unhydrated cloud shortcut: Even after an Outlook error window closes, OUTLOOK.EXE often stays frozen in the background, holding an exclusive write lock on your .pst file. Press Ctrl + Shift + Esc, open Task Manager, and terminate any running Microsoft Outlook process before scanning. If your file displays a OneDrive cloud icon (Files On-Demand), right-click it and choose Always keep on this device so the full binary file downloads to your local drive before recovery.
Every Outlook database follows the binary MS-PST specification, beginning with a 4-byte file signature (!BDN / hex 0x21 0x42 0x44 0x4E) and two internal B-tree directories: the Node B-Tree (NBT), which stores folder hierarchy links (Parent NID) and item descriptors, and the Block B-Tree (BBT), which maps physical data clusters containing message bodies and attachments.
| Outlook Error or Symptom | Damaged Internal Node | Algorithm Action | Recovery Outcome |
|---|---|---|---|
| Not a Personal Folders file | Corrupted !BDN header bytes |
Bypasses header; scans raw blocks | Full folder tree rebuilt |
| Cannot open the set of folders | Broken Node B-Tree (NBT) links | Relinks Parent NID descriptors |
Original hierarchy preserved |
| Cyclic Redundancy Check (CRC) | Unreadable Block B-Tree sector | Skips bad sector; reads healthy blocks | Intact emails & files rescued |
| 2 GB (ANSI) or 50 GB+ freeze | 32-bit or registry size ceiling | Streams pages sequentially | Clean Unicode PST output |
| Orphaned or crashed .OST file | Broken Exchange/IMAP sync lock | Parses offline cache in cloud app | Converts .OST data to .PST |
| Emptied Deleted Items / folders | Removed NBT directory entry | Carves unallocated BBT clusters | Deleted items restored |
!BDN header or upper NBT index pages, simple utilities either delete damaged clusters or dump surviving messages into a single chaotic Lost and Found folder without subfolder names. Our algorithm scans leaf NBT records and raw BBT data blocks from the bottom up, matching every email, contact, and calendar entry back to its original Parent NID folder descriptor.Both the browser service and PST Repair Kit for Windows restore the full spectrum of MAPI objects across legacy ANSI and modern Unicode databases (supporting Outlook 97 through Outlook 2024 and Microsoft 365):
| Mailbox Object Type | Restored Data & Metadata | Engine Support | Verification in Free PST Viewer |
|---|---|---|---|
| Emails & Headers | HTML, RTF, Text; To, Cc, Bcc, UTF-8 | Full recovery | Read message body in preview |
| Attachments & Inline Files | PDFs, Office docs, images, nested MSG | Full recovery | Check attachment list per email |
| Contacts & Address Lists | Names, emails, phone numbers, notes | Full recovery | Open Contacts folder in tree |
| Calendar & Appointments | Events, recurring series, attendees | Full recovery | Inspect Calendar dates & titles |
| Tasks, Notes & Journals | To-do items, sticky notes, timestamps | Full recovery | Browse Tasks and Notes |
| Deleted & Orphaned Items | Items deleted before file compaction | Carved from slack | Check restored items in folders |
Rescuing non-synced "This Computer Only" Contacts & Calendars from IMAP .OST files: In Outlook 2013, 2016, 2019, 2021, 2024, and Microsoft 365, accounts configured via IMAP (including Gmail, Yahoo! Mail, Hotmail/Outlook.com, and corporate IMAP servers) store their local database in an .ost file. While email folders synchronize with the mail server, Outlook stores your local address book and calendar inside folders labeled Contacts (This computer only) and Calendar (This computer only) that never back up to the cloud. If your IMAP profile corrupts or your server account closes, upload that .ost file to our Online Recovery Service ($10/GB) to extract those local contacts, calendar appointments, and cached emails into a clean .pst file.
To evaluate your file accurately before paying, review how our engine handles passwords, message-level certificates, and physical disk damage:
Both workflows operate in strict read-only mode on your damaged source file, leaving the original database untouched while building a brand-new .pst container:
Step 1 — Run a Read-Only Binary Scan: Upload your damaged .pst or .ost file to the online analyzer at the top of this page (from any mobile or desktop browser), or launch PST Repair Kit on your Windows PC and select your local .pst file.
Step 2 — Verify Your Data in the Free PST Viewer & Demo Output: Once scanning finishes, expand the restored folder hierarchy on the free preview screen (Free PST Viewer) to read emails and check contacts, calendars, and attachments. In the online service, click Download Demo File on the preview page to test a sample .pst file; in the Windows demo of PST Repair Kit, click export to save up to 5 recovered objects per folder to your local drive for free.
Step 3 — Unlock Full Export & Mount Safely in Outlook: Pay $10 per 1 GB in the online service to download the complete repaired database, or activate a PST Repair Kit license (from $39) on Windows to remove the 5-item-per-folder demo restriction and save unlimited files of any size.
Before paying for full recovery, spend 60 seconds checking these four indicators during Step 2:
3. Message Bodies, UTF-8 Text & Attachments: Click several emails in the Free PST Viewer pane to verify clean HTML/RTF text rendering, non-English UTF-8 characters, and listed file attachments.
Never use Outlook's Import and Export Wizard (File > Open & Export > Import/Export) to load a repaired database or demo file—the Import Wizard merges folders into your active mailbox and overwrites existing emails that share the same subject line. Instead, always mount the repaired .pst as a separate, read-safe folder tree:
In the "New Outlook" App on Windows 11: Click the Settings (Gear Icon) in the top-right corner, navigate to Files > Outlook Data Files (or Accounts > Storage), and click Add .pst file to attach the repaired database (or toggle the New Outlook switch in the top-right corner back to Classic Outlook for full local PST control).
With PST Repair Kit you can fix next errors:
The file outlook.pst is not a Personal Folders File.
0x80040116.
The file Outlook.pst cannot be opened.
80040818 when trying to repair the PST file.
Microsoft Outlook has encountered a problem and needs to close. We are sorry for the inconvenience.
0x80070570: The file or directory is corrupted and unreadable.0x8004060C): Unknown Error 0x8004060CSystem requirements:
01 FAQ#
Yes. Previous repair attempts or backup utilities often leave a replica of your database in the same directory with a .bak extension (such as outlook.bak or mailbox.pst.bak). Make a copy of that file in Windows File Explorer, rename its extension from .bak to .pst (for example, mailbox_backup.pst), and open it in PST Repair Kit on Windows or upload it to the online service on this page. Because our algorithm parses raw NBT and BBT blocks directly, it frequently recovers folders and emails from the .bak copy that other utilities missed.
02 FAQ#
Scanning a 15 GB to 50+ GB Unicode database requires inspecting millions of 64-bit binary blocks to relink folder descriptors and carve deleted items, which typically takes between 30 minutes and 2 - 3 hours on a modern Windows PC depending on CPU, RAM, and drive speed. For maximum speed on multi-gigabyte archives: (1) store both the source file and output file on a local TFS SSD with at least 2.5x the source file size in free space, (2) close Outlook and memory-heavy applications, and (3) temporarily pause real-time antivirus scanning on your working folder so the antivirus filter does not intercept every individual block read/write operation.
03 FAQ#
When you mount a newly repaired multi-gigabyte .pst file in Outlook, the background Windows Search service must build a fresh full-text index of its contents before instant search returns matches. Depending on file size, indexing takes 15 to 60 minutes (you can check progress in Outlook under File > Options > Search > Indexing Options); while Windows indexes the file, you can browse and sort all folders by date or sender immediately. Furthermore, our algorithm preserves both external SMTP headers and internal Microsoft Exchange addressing attributes (LegacyExchangeDN / X500), ensuring that clicking Reply on restored corporate emails works cleanly.
04 FAQ#
Both file-size changes are normal behaviors of the MS-PST binary format. A repaired .pst file is often 20% to 50% smaller than the damaged source database because years of deleting emails and moving folders leave behind gigabytes of fragmented "white space" (slack sectors) that our engine strips out when writing a clean, compact Unicode .pst file. Conversely, the output file can become slightly larger than the original if the algorithm carves and restores previously deleted emails and attachments from unallocated blocks back into visible folders.
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