Guide

PST & OST: Complete Guide to Microsoft Outlook Data Files

PC By Pablo Cirre • Updated May 7, 2026

PST & OST: Complete Guide to Microsoft Outlook Data Files

For millions of Microsoft Outlook users, the PST file is the unsung keeper of their digital work life — storing years of emails, contacts, calendar appointments, and tasks in a single binary file on their hard drive. PST files are reliable enough that many people never think about them until something goes wrong. When it does, understanding what PST and OST files are, how they work, and how to repair, export, or migrate them becomes urgent.

What Is a PST File?

PST (Personal Storage Table) is Microsoft Outlook's local data file format. It stores a complete mailbox — email messages, folders, contacts, calendar items, tasks, notes, and journal entries — in a single proprietary file on your local disk.

PST files are used for:

Local email archiving: storing old emails offline to keep the mailbox size manageable
Standalone (non-Exchange) accounts: POP3 email accounts store all mail in a PST file
Personal archive: deliberately moving items out of the server mailbox for long-term retention

Two Generations of PST Format

ANSI PST (Outlook 97-2002): The original PST format, limited to 2 GB maximum. Files that approach this limit corrupt silently as Outlook continues writing past the safe threshold. If you have a very old PST file, this is the version you have.

Unicode PST (Outlook 2003 and later): The modern format, supporting files up to 50 GB by default (configurable up to 100 GB via registry). All new PST files created by Outlook 2003+ use Unicode format. This is the format you should be using.

Default PST File Location

On Windows 10/11 with Outlook 2016+:

C:\Users\[username]\AppData\Local\Microsoft\Outlook\[email-address].pst

On older Windows versions or Outlook 2010:

C:\Users\[username]\Documents\Outlook Files\[email-address].pst

Find your PST location in Outlook: File → Account Settings → Account Settings → Data Files tab.

What Is an OST File?

OST (Offline Storage Table) is the local cache file that Outlook creates when connected to an Exchange Server, Microsoft 365, or an IMAP account. Unlike PST (which is the primary storage), OST is a synchronized mirror of your server mailbox:

OST is automatically managed by Outlook: it syncs changes between the server and local cache
You cannot add an OST to another Outlook installation: OST files are tied to the specific Exchange account that created them
Deleting the OST is safe if you have server access: Outlook will rebuild it by re-syncing from the server
If you lose server access, your OST becomes your only copy — treat it carefully

OST File Location

C:\Users\[username]\AppData\Local\Microsoft\Outlook\[email-address].ost

PST vs OST: Key Differences

Feature	PST	OST
Primary use	Local archive / POP3 mail	Exchange/Microsoft 365 cache
Data authority	PST is the master copy	Server is the master copy
Portability	Can be opened on any Outlook	Tied to originating account
Size limit	50 GB (Unicode format)	50 GB (same format internally)
Rebuilding	Cannot be rebuilt — data loss if lost	Rebuild by re-syncing from server
When server unavailable	Primary offline storage	Read/write locally, sync when reconnected
Export	Manually managed	Automatically managed by Outlook

Common PST Problems and Fixes

Corrupt PST File

Corruption causes: abrupt Outlook termination, disk errors, antivirus scanning open PST, PST approaching the 2 GB ANSI limit.

ScanPST.exe (Inbox Repair Tool) is included free with every Outlook installation:

Location:

Outlook 2019/Microsoft 365: C:\Program Files\Microsoft Office\root\office16\SCANPST.EXE
Outlook 2016: C:\Program Files (x86)\Microsoft Office\Office16\SCANPST.EXE

Using ScanPST:

Close Outlook completely
Run SCANPST.EXE
Browse to your PST file location
Click Start to scan
If errors found, click Repair
ScanPST creates a backup (.bak) before repairing

For severely corrupt files where ScanPST fails, third-party tools like Stellar Repair for Outlook, Kernel for Outlook PST Repair, or DataNumen Outlook Repair may recover more data.

PST File Too Large

If your PST is approaching 50 GB or if Outlook performance has slowed:

Create a new PST archive: File → New → Outlook Data File → choose a different name
Move old email: select old folders or date-filtered items → Move to Folder → choose the new PST
Use AutoArchive: Outlook's built-in tool to automatically move old items to an archive PST based on age (File → Options → Advanced → AutoArchive Settings)
Compact the PST: after deleting items, reclaim space with File → Account Settings → Data Files → Settings → Compact Now

Cannot Open PST (Access Denied)

This occurs when antivirus software has locked the file, another application is using it, or file permissions are incorrect. Try: reboot, disable real-time antivirus scanning for the Outlook folder, or take ownership of the file (Windows Security → Properties → Security tab → Advanced → Change owner).

Exporting PST Contents

Export to EML (Individual Emails)

Outlook does not natively export individual emails as EML in bulk. Options:

Drag-and-drop: drag emails from Outlook to a folder in Windows Explorer — Outlook saves them as .msg files, not .eml
Import/Export Wizard: File → Open & Export → Import/Export → Export to a File → Comma Separated Values (for contacts/calendar) or to another Outlook data file (another PST)
Free tools: MailStore Home, PSTwalker, or Aid4Mail can export PST to EML format

Export to PDF

Individual emails can be printed to PDF (Ctrl+P → Microsoft Print to PDF). For bulk export to PDF:

MailStore Home (free for personal use): converts PST contents to searchable PDF
Third-party tools like PST to PDF Converter (paid)

Migrating PST to Gmail, Office 365, or Thunderbird

PST → Gmail: use Google Workspace Migration for Microsoft Outlook (GWMMO) — free tool from Google PST → Thunderbird: Thunderbird with ImportExportTools NG can import PST files directly PST → Office 365 (new tenant): use the Office 365 Import Service (requires tenant admin access)

Opening PST Without Outlook

Several approaches work without a Microsoft Office subscription:

Thunderbird + ImportExportTools NG plugin: import PST/OST files directly (some PST files require the companion libpff integration)
LibPST / readpst (Linux, also available for Windows): readpst -o output_dir/ mailbox.pst — extracts to mbox format
MFCMAPI (Microsoft's free developer tool): low-level access to PST/OST contents, including raw message properties
Online converters: upload PST and download EML, PDF, or other formats (use only for non-sensitive data)

PST in Legal and Compliance Contexts

PST files are the default output format for e-discovery requests in legal proceedings. Organizations routinely receive legal holds requiring preservation of PST files for litigation. Key considerations:

Metadata preservation: MSG messages inside PST preserve full Internet headers, including received timestamps and routing information — essential for forensic authenticity
Chain of custody: PST files should be hashed (SHA-256) before and after review to demonstrate no modification
E-discovery tools: Relativity, Nuix, and Veritas eDiscovery Platform all ingest PST/OST natively
Microsoft's recommendation: move from local PST files to Exchange Online / Microsoft 365 for better compliance, audit logging, and litigation hold capabilities

PST files are like a filing cabinet living on your hard drive: capacious, reliable when healthy, but a single point of failure if the drive dies. Regular backups of your PST files (along with the emails in them) are one of the most underrated personal data management practices.

Related conversions

Frequent conversions across the catalogue:

Frequently Asked Questions

PST (Personal Storage Table) is Outlook's local archive file — it stores emails, contacts, and calendar items locally on your hard drive. It is the primary data store for POP3 accounts and serves as an offline archive for Exchange accounts. OST (Offline Storage Table) is a synchronized cache of your Exchange or Microsoft 365 mailbox — the server is the master copy and OST is the local mirror. You can copy and open a PST on any Outlook installation; an OST is tied to the specific account that created it and cannot be opened independently.

PST (Personal Storage Table) is Outlook's local archive arquivo — it stores emails, contacts, e calendar items locally on your hard drive. It is the primary data store para POP3 accounts e serves as an offline archive para Exchange accounts. OST (Offline Storage Table) is a synchronized cache of your Exchange ou Microsoft 365 mailbox — the server is the master copy e OST is the local mirror. You can copy e abrir a PST on any Outlook installation; an OST is tied para o specific account that created it e cannot be opened independently.

PST (Personal Storage Table) ist Outlooks lokales Archiv — speichert E-Mails, Kontakte und Kalendereinträge lokal auf der Festplatte. Es ist der primäre Datenspeicher für POP3-Konten und dient als Offline-Archiv für Exchange-Konten. OST (Offline Storage Table) ist ein synchronisierter Cache deines Exchange- oder Microsoft-365-Postfachs — der Server hat die Master-Kopie und OST ist nur das lokale Spiegelbild. Eine PST kann auf jeder Outlook-Installation kopiert und geöffnet werden; eine OST hingegen ist an das spezifische Konto gebunden, das sie erstellt hat, und kann nicht unabhängig geöffnet werden.

PST (Personal Storage Table) es el archivo local de Outlook donde se guardan correos, contactos y eventos del calendario en tu disco. Es el almacén principal para cuentas POP3 y sirve como archivo offline para cuentas Exchange. OST (Offline Storage Table) es una caché sincronizada de tu buzón Exchange o Microsoft 365 — el servidor mantiene la copia maestra y el OST es solo el espejo local. Puedes copiar y abrir un PST en cualquier instalación de Outlook; en cambio, un OST está vinculado a la cuenta específica que lo creó y no puede abrirse de forma independiente.

On KaijuConverter every file is processed inside an isolated container, encrypted in transit (TLS 1.3) and at rest, and automatically deleted after 60 minutes with multi-pass overwrite. We never train on, share, or analyze user content. For maximum privacy on extremely sensitive material, prefer offline tools (ImageMagick, FFmpeg, LibreOffice) that you control end-to-end.

Use ScanPST.exe (Inbox Repair Tool), which is included free with every Outlook installation. Find it at: Outlook 2019/365: C:\Program Files\Microsoft Office\root\office16\SCANPST.EXE. Steps: (1) close Outlook completely, (2) run SCANPST.EXE, (3) browse to your .pst file, (4) click Start, (5) if errors are found, click Repair. ScanPST creates a .bak backup first. For severely corrupt files that ScanPST cannot fix, third-party tools like Stellar Repair for Outlook may recover more data.

For 95% of use cases, yes — server-side ImageMagick, FFmpeg and LibreOffice produce identical output to the same tools on your laptop. Desktop software wins for: extremely large files (multi-GB), batch jobs of thousands of files, scripted pipelines, or content too sensitive to upload. KaijuConverter caps at 25 MB per file on the free tier (up to 2 GB on paid plans).

For EML: Outlook does not bulk-export to EML natively. Use the free tool MailStore Home, which can read a PST file and export every email as an individual .eml file with full metadata. Alternatively, install Thunderbird with ImportExportTools NG plugin, which can import PST and export as EML or mbox. For PDF: MailStore Home also creates searchable PDFs. Individual emails can be printed to PDF using Ctrl+P → Microsoft Print to PDF.

For EML: Outlook does not bulk-export to EML natively. usar the grátis tool MailStore Home, which can read a PST arquivo e export every email as an individual .eml arquivo com full metadata. Alternatively, install Thunderbird com ImportExportTools NG plugin, which can import PST e export as EML ou mbox. para PDF: MailStore Home also creates searchable PDFs. Individual emails can be printed to PDF usando Ctrl+P → Microsoft Print to PDF.

For EML: Outlook does not bulk-export to EML natively. verwenden the kostenlos tool MailStore Home, which can read a PST Datei und export every email as an individual .eml Datei mit full metadata. Alternatively, install Thunderbird mit ImportExportTools NG plugin, which can import PST und export as EML oder mbox. für PDF: MailStore Home also creates searchable PDFs. Individual emails can be printed to PDF using Ctrl+P → Microsoft Print to PDF.

For EML: Outlook does not bulk-export to EML natively. usar the gratis tool MailStore Home, which can read a PST archivo y export every email as an individual .eml archivo con full metadata. Alternatively, install Thunderbird con ImportExportTools NG plugin, which can import PST y export as EML o mbox. para PDF: MailStore Home also creates searchable PDFs. Individual emails can be printed to PDF using Ctrl+P → Microsoft Print to PDF.

Most format conversions are lossy by design — JPG, MP3, MP4, WebP all discard perceptual data to save bytes. Going through a lossy intermediate compounds the loss. To minimize visible/audible drift: convert from the original master, choose a higher quality setting, and avoid converting back and forth between lossy formats.

Yes. Thunderbird (free) with the ImportExportTools NG plugin can import PST files directly. On Linux, the libpst package provides the readpst command: `readpst -o output_folder/ mailbox.pst` — this extracts all emails to mbox format. The free Microsoft developer tool MFCMAPI provides low-level access to PST contents. For contacts specifically, you can import the PST into Outlook, then export contacts as CSV. For email forensics, tools like Autopsy and FTK read PST files natively.

Yes. Thunderbird (free) com the ImportExportTools NG plugin can import PST arquivos directly. no Linux, the libpst package fornece the readpst command: `readpst -o output_folder/ mailbox.pst` — this extracts all emails to mbox formato. The grátis Microsoft developer tool MFCMAPI fornece baixa-level access to PST contents. para contacts specifically, you can import the PST em Outlook, then export contacts as CSV. para email forensics, ferramentas like Autopsy e FTK read PST arquivos natively.

Yes. Thunderbird (free) mit the ImportExportTools NG plugin can import PST Dateien directly. auf Linux, the libpst package bietet the readpst command: `readpst -o output_folder/ mailbox.pst` — this extracts all emails to mbox Format. The kostenlos Microsoft developer tool MFCMAPI bietet niedrig-level access to PST contents. für contacts specifically, you can import the PST in Outlook, then export contacts as CSV. für email forensics, Werkzeuge like Autopsy und FTK read PST Dateien natively.

Yes. Thunderbird (free) con the ImportExportTools NG plugin can import PST archivos directly. en Linux, the libpst package proporciona the readpst command: `readpst -o output_folder/ mailbox.pst` — this extracts all emails to mbox formato. The gratis Microsoft developer tool MFCMAPI proporciona baja-level access to PST contents. para contacts specifically, you can import the PST en Outlook, then export contacts as CSV. para email forensics, herramientas like Autopsy y FTK read PST archivos natively.

Yes — KaijuConverter accepts multiple files in a single drop and returns a ZIP. For very large batches (thousands of files) consider command-line tools or our API: <code>find . -name "*.heic" -exec magick {} {.}.jpg \;</code> or similar one-liners scale to millions of files when run locally.