File Extension Guide📖 What is a PST File?
A PST file (Personal Storage Table), also known as a Personal Folders file, is Microsoft Outlook's proprietary file format for storing copies of messages, calendar events, contacts, tasks, and other items locally on your computer.
Introduced with Microsoft Outlook 97, PST files have become the standard way to backup, archive, and transfer Outlook data. Unlike server-based storage, PST files give users complete control over their email data, allowing them to store information independently of their email provider or corporate Exchange server.
Communication Data
- Email messages (sent & received)
- Email attachments
- Email folder structure
- Message rules and settings
Personal Information
- Contacts and address books
- Calendar appointments & meetings
- Tasks and to-do lists
- Notes and journal entries
⚡ Quick Facts
| File Extension | .pst |
| Full Name | Personal Storage Table (Personal Folders File) |
| Category | Email Data / Outlook Data File |
| MIME Type | application/vnd.ms-outlook |
| Developed By | Microsoft Corporation |
| First Released | 1997 (with Outlook 97) |
| File Type | Binary (proprietary structured format) |
| Current Format | Unicode PST (Outlook 2003+) |
| Max Size (Unicode) | 50GB default (can be increased) |
| Max Size (ANSI) | 2GB (legacy format) |
| Encryption | Optional (Compressible, High encryption) |
| Password Protection | Yes (not highly secure) |
📦 What a PST File Stores
PST files are comprehensive data containers that can store virtually all types of Outlook data:
Email Messages
Inbox, Sent, Drafts, and custom folders with full message content and headers
Attachments
All file attachments embedded within email messages
Calendar
Appointments, meetings, events, and recurring schedules
Contacts
Address book entries with photos, details, and distribution lists
Tasks
To-do items with due dates, priorities, and completion status
Notes
Sticky notes and quick reminders created in Outlook
📁 Typical PST Folder Structure
├── 📁 Inbox , Received emails
├── 📁 Sent Items , Sent emails
├── 📁 Drafts , Unsent messages
├── 📁 Deleted Items , Trash
├── 📁 Calendar , Appointments & meetings
├── 📁 Contacts , Address book
├── 📁 Tasks , To-do items
├── 📁 Notes , Sticky notes
├── 📁 Journal , Activity log
└── 📁 Custom Folders... , User-created folders
⚖️ PST vs OST
Outlook uses two different local storage formats. Understanding the difference is crucial for managing your email data:
| Feature | PST (Personal Storage Table) | OST (Offline Storage Table) |
|---|---|---|
| Purpose | Backup, archive, data portability | Offline cache of server mailbox |
| Creation | Manually created by user | Automatically created by Outlook |
| Server Sync | ❌ Independent of server | ✅ Syncs with Exchange/M365 |
| Portability | ✅ Can be moved/copied anywhere | ❌ Tied to Outlook profile |
| Use Case | Backup, migration, archival | Working offline with server mail |
| Data Recovery | Direct access to all data | Must reconnect to server or convert |
| Account Types | Any (POP3, IMAP, Exchange) | Exchange/Microsoft 365 only |
| File Location | User-defined | Fixed location in AppData |
- Create backups of important emails
- Archive old messages to save server space
- Transfer data between computers
- Store data independently of email account
- Share mailbox data with others
- Working offline with Exchange/M365 account
- Outlook needs to cache server data locally
- You want automatic sync with server
- Using Cached Exchange Mode
- Temporary offline access is needed
📊 PST File Versions
Microsoft has released two major versions of the PST format, with significant differences in capabilities:
Legacy Format
Outlook 97 - 2002
- Maximum size: 2GB
- ANSI character encoding
- Limited international support
- 32-bit internal pointers
- Prone to corruption near limit
Modern Format
Outlook 2003 - Present
- Maximum size: 50GB+
- Unicode character support
- Full international language support
- 64-bit internal pointers
- More robust and reliable
Outlook Version Compatibility
Outlook 2003 and Later
Creates Unicode PST files by default. Can read both ANSI and Unicode formats. Recommended to convert old ANSI files to Unicode for better reliability.
Outlook 97, 98, 2000, 2002
Only creates and reads ANSI PST files. Cannot open Unicode PST files. These versions are obsolete and should be upgraded.
📏 PST Size Limits
Understanding PST size limits is crucial for avoiding data loss and performance issues:
Size Comparison
ANSI PST (Legacy), Max 2GB
Unicode PST (Default), Max 50GB
Recommended Size, Under 10GB
⚠️ What Happens at Size Limit?
- ANSI PST at 2GB: File becomes corrupted, data loss likely
- Unicode PST at limit: Outlook refuses to add more data
- Performance degradation: Slow searching, opening, syncing
- Increased corruption risk: Larger files are more vulnerable
✅ Best Practices for Size Management
- Keep under 10GB: Microsoft's recommendation for optimal performance
- Regular archiving: Move old items to separate archive PST files
- Compact regularly: Remove deleted space using compact feature
- Monitor size: Check file properties periodically
MaxLargeFileSize and WarnLargeFileSize values). However, Microsoft recommends against exceeding 50GB due to performance concerns.
📂 How to Open a PST File
There are several ways to open and access PST files depending on your available software:
Microsoft Outlook
Native support, best compatibility
Without Outlook
Free viewers for read-only access
Alternative Clients
*Requires ImportExportTools add-on
Convert First
Convert to universal formats
Opening PST in Microsoft Outlook
- Open Microsoft Outlook on your computer.
- Click File in the top menu bar.
- Select Open & Export from the left sidebar.
- Click "Open Outlook Data File" option.
- Navigate to your PST file and select it.
- Access the PST, it appears in your folder pane on the left side as a separate mailbox.
Opening PST Without Outlook
Using Free PST Viewer:
- Download a PST viewer like Univik PST Viewer (free).
- Install and launch the viewer application.
- Click "Open" or "Add File" and select your PST file.
- Browse the contents, view emails, contacts, calendar items.
- Export if needed, many viewers allow export to other formats.
📍 Default PST File Locations
PST files are typically stored in specific locations depending on your Windows version and Outlook configuration:
Windows 10 / 11 Default Location:
Older Windows Versions:
C:\Users\<YourUsername>\AppData\Local\Microsoft\Outlook\
Windows XP:
C:\Documents and Settings\<YourUsername>\Local Settings\Application Data\Microsoft\Outlook\
How to Find Your PST File Location in Outlook
Method 1: Account Settings
- Open Outlook
- Click File → Account Settings → Account Settings
- Select the Data Files tab
- Your PST files are listed with their full paths
Method 2: Right-Click Folder
- In Outlook, right-click on the PST folder name
- Select Data File Properties
- Click the Advanced button
- The file path is shown in the Filename field
🔧 Repair & Recovery
PST files can become corrupted due to various reasons. Microsoft provides a built-in repair tool:
📦 ScanPST.exe (Inbox Repair Tool)
Microsoft's official free tool for repairing corrupted PST files. It's installed automatically with Outlook.
Location by Outlook Version:
C:\Program Files\Microsoft Office\root\Office16\SCANPST.EXE
Outlook 365/2021/2019 (32-bit):
C:\Program Files (x86)\Microsoft Office\root\Office16\SCANPST.EXE
Outlook 2016:
C:\Program Files (x86)\Microsoft Office\Office16\SCANPST.EXE
Outlook 2013:
C:\Program Files (x86)\Microsoft Office\Office15\SCANPST.EXE
⚠️ Common Causes of Corruption
- Exceeding size limits (especially ANSI 2GB)
- Improper Outlook shutdown
- Hardware failures
- Network issues (PST on network drive)
- Malware or virus infections
- Software conflicts
How to Use ScanPST.exe
- Close Outlook completely (check Task Manager to ensure it's not running).
- Navigate to ScanPST.exe using the paths above and double-click to run it.
- Click Browse and select the corrupted PST file.
- Click Start to begin the scanning process.
- Review results, if errors are found, click Repair.
- Check "Make backup" option before repairing (recommended).
- Run multiple times if needed, severe corruption may require repeated repairs.
🎯 Common Uses
PST files serve many important purposes in personal and business email management:
Email Backup
Create complete backups of your Outlook mailbox including emails, contacts, and calendar.
Email Archiving
Move old emails to archive PST files to reduce mailbox size and improve performance.
Data Migration
Transfer Outlook data between computers, accounts, or when switching email providers.
Legal Discovery
Extract and analyze email communications for legal proceedings and compliance audits.
Compliance Storage
Meet regulatory requirements for email retention in finance, healthcare, and legal industries.
Offline Access
Access important emails and contacts without internet connection by storing in local PST.
✅ PST Best Practices
Follow these recommendations to keep your PST files healthy and your data safe:
✅ Do
- Keep files under 10GB for optimal performance
- Store PST on local drives (SSD preferred)
- Back up PST files regularly to external storage
- Use Unicode format (Outlook 2003+)
- Compact PST periodically to reclaim space
- Close Outlook properly before shutting down
- Run ScanPST if you notice issues
❌ Don't
- Don't store PST on network drives, causes corruption
- Don't let PST exceed 50GB without splitting
- Don't rely solely on PST password for security
- Don't ignore performance slowdowns
- Don't store PST on removable drives while in use
- Don't open same PST from multiple computers
- Don't skip backups, corruption happens
🔧 Troubleshooting
Common PST file issues and their solutions:
- Wrong file type: Ensure you're opening a .pst file, not .ost or other format
- Corruption: Run ScanPST.exe to repair the file
- Version mismatch: File may be from newer Outlook version, try updating
- Incomplete download: Re-download or re-copy the file
- Outlook still running: Close Outlook completely (check Task Manager)
- Background processes: End OUTLOOK.EXE in Task Manager
- Antivirus scanning: Temporarily disable or add exclusion
- File locked: Restart computer to release file locks
- File too large: Archive old items to reduce size below 10GB
- Fragmented file: Compact the PST (File → Data File Management → Compact)
- Network location: Move PST to local drive
- Too many items in folders: Organize into subfolders
- Search indexing: Rebuild Outlook search index
- Password recovery tools: PST password protection is weak, tools like PstPassword can recover it
- Create new PST: If using Exchange, create new PST and export from server
- Note: PST passwords provide minimal security, anyone with tools can bypass them
- Not opened: Use File → Open → Outlook Data File to add PST
- Hidden folders: Expand all folders in the PST in folder pane
- Corrupted during transfer: Re-copy and verify file size matches original
- Run ScanPST: Repair any issues from transfer
❓ Frequently Asked Questions
Partially. Microsoft Outlook for Mac has limited PST support:
- Outlook for Mac 2016+: Can import PST files (File → Import → Outlook for Windows archive)
- Limitation: Cannot open PST directly, must import into Mac mailbox
- Alternative: Use PST viewers or convert to MBOX format first
- Best option: Import on Windows Outlook, then export to format Mac can use
To merge PST files in Outlook:
- Open both PST files in Outlook simultaneously
- Select items from source PST (Ctrl+A for all in a folder)
- Move to destination: Right-click → Move → Other Folder → select destination PST
- Repeat for each folder you want to merge
- Alternative: Use dedicated PST merge tools for bulk operations
PST encryption and passwords are NOT highly secure. Consider these points:
- Password protection: Easily bypassed with free tools, provides minimal security
- Compressible encryption: Weak, can be cracked
- High encryption: Better but still not enterprise-grade
- For true security: Use full-disk encryption (BitLocker), store on encrypted drives, or use enterprise archiving solutions
To split a PST file into smaller files:
- Create new PST: File → New → Outlook Data File
- Move items: Drag folders or emails from old PST to new one
- By date: Create archive PSTs for each year
- Automation: Use Outlook's AutoArchive feature with date rules
- Third-party tools: PST splitter utilities can automate by size or date
Yes! PST files can be converted to many formats:
- PST to MBOX: For Thunderbird, Apple Mail, and Unix clients
- PST to EML: Individual email files for any client
- PST to PDF: For documentation and legal purposes
- PST to MSG: Outlook message format
- Use PST Converter tools for batch conversion
PST files don't automatically shrink when you delete items. You need to:
- Empty Deleted Items: Right-click Deleted Items → Empty Folder
- Compact the PST: File → Account Settings → Data Files → Select PST → Settings → Compact Now
- Enable auto-compact: Outlook compacts files when closed if 20%+ is recoverable
- Note: Compacting can take time for large files
PST files are designed for desktop Outlook and don't work directly on mobile or web:
- Mobile: No direct access, import PST to email server, then sync to mobile
- Web: Some online PST viewers exist but limited functionality
- Best approach: Import PST into IMAP account or Microsoft 365, then access anywhere
- Outlook.com: Can import PST files for web access
🛠️ Related Tools
📝 Summary: Key Points About PST Files
- PST (Personal Storage Table) is Outlook's local data format
- Stores emails, contacts, calendar, tasks in one file
- Unicode format supports up to 50GB (expandable)
- ANSI format (legacy) has 2GB limit
- Best kept under 10GB for performance
- ScanPST.exe repairs corrupted files
- Store on local drives, not network shares
- Different from OST (offline cache for Exchange)
- Can be opened without Outlook using viewers
- Back up regularly, corruption happens
- Password protection is weak, use disk encryption
- Portable format for backup and migration
