PST File Format

Overview

Outlook PST files are a cornerstone of email management for millions of users worldwide. These Personal Storage Table (PST) files serve as digital vaults for your emails, calendar entries, contacts, tasks, and notes—essentially storing everything you need in one place. Whether you’re an individual user looking to archive years’ worth of correspondence or a business managing large volumes of data, PST files offer a robust solution. The format’s longevity and widespread adoption make it indispensable for anyone working with Microsoft Outlook.

PST files come in two flavors: ANSI (older) and Unicode (modern). While the older ANSI version is limited to 2 GB per file, the Unicode variant can handle up to 50 GB, making it ideal for today’s data-heavy environments. Despite their age, PST files remain relevant due to their compatibility with a wide range of applications and platforms.

Key Features

  • Extensive Data Storage: Holds emails, calendar items, contacts, tasks, and more.
  • Unicode Support: Modern Unicode version supports larger file sizes up to 50 GB.
  • Hierarchical Structure: Organized into folders for easy navigation and management.
  • Compatibility Across Platforms: Works seamlessly with Windows and some Linux applications.
  • Security Options: Password protection ensures data privacy.

Technical Specifications

Format Structure

PST files are binary in nature, following a structured format that includes headers, body sections, and various data structures. The file is organized into layers for efficient storage and retrieval of information.

Core Components

Header Information

The PST header begins with the magic word !BDN, followed by metadata such as version numbers (wVer), client versions (wVerClient), and platform identifiers (bPlatformCreate, bPlatformAccess). The header also includes a unique identifier (dwUnique) that changes each time the file is modified, ensuring data integrity.

Node Database (NDB) Layer

The NDB layer forms the backbone of PST files. It contains headers, allocation information, blocks, and B-Trees which are crucial for managing storage efficiently. Data BIDs link nodes and blocks within this layer.

Lists, Tables, and Properties (LTP) Layer

This layer provides a logical understanding of higher-level concepts such as Property Contexts (PC) and Table Contexts (TC). PCs and TCs utilize Heap On Node (HN) and BTree on Heap (BTH) data structures for efficient implementation.

Messaging Layer

The messaging layer implements high-level rules and business logic, resulting in Folder objects, Message objects, and Attachment objects. This layer combines the functionality of LTP and NDB layers to provide a comprehensive view of PST content.

Standards & Compatibility

PST files adhere to standards set by Microsoft under the Open Specification Promise (OSP), ensuring free access to specifications without licensing fees. The format supports both ANSI and Unicode versions, with backward compatibility for older applications like Outlook 2002 and earlier.

History & Evolution

The PST file format was introduced in the early days of Microsoft Outlook as a means to store user data offline. Over time, it evolved to support larger filesizes and more robust security features. Major milestones include:

  • 1998: Introduction of ANSI PST files with a 2 GB limit.
  • Late 2000s: Release of Unicode PST files, removing the file size limitation.
  • Present Day: Continued use in modern versions of Outlook alongside newer formats like OST (Offline Storage Table) for email synchronization.

Working with PST Files

Opening PST Files

You can open PST files using Microsoft Outlook on Windows and macOS. Third-party tools such as Unlock PST and Kernel for PST are also available, though they may require specific licenses or subscriptions.

Converting PST Files

Common conversion scenarios include moving data to cloud storage solutions like Office 365 or transferring emails between different email clients. Tools like PST Viewer Pro and SysTools Outlook PST Converter can help with these tasks without needing to install additional software on your system.

Creating PST Files

PST files are typically created by exporting data from Microsoft Outlook. You can also use third-party tools designed for bulk export operations, especially useful in enterprise environments where large volumes of email need archiving.

Common Use Cases

  • Email Archival: Storing years’ worth of emails and attachments.
  • Data Migration: Moving email data between different versions of Outlook or other email clients.
  • Backup Solutions: Creating backups for critical business communications and documents.

Data Protection

PST files can be password protected, but this method offers limited security. The password is stored as a CRC-32 hash and does not provide strong encryption against unauthorized access. For enhanced data protection, consider using additional third-party tools or cloud-based solutions that offer stronger encryption methods.

References

 English