What Is a PST File? How to Open, Read, and Convert It

What Is a PST File?

A PST file — short for Personal Storage Table — is a proprietary data file format created by Microsoft for its Outlook email client. It acts as a local database that stores a complete copy of your mailbox data directly on your computer. If you have ever used Outlook on Windows, chances are you already have one or more PST files sitting on your hard drive.

PST files use the .pst extension and follow the Microsoft Open Specification (MS-PST). While the specification is publicly documented, the format itself is complex and tightly coupled to the Outlook ecosystem. This makes PST files easy to use inside Outlook but notoriously difficult to work with outside of it.

What Is Inside a PST File?

A PST file is not just a collection of emails. It is a structured database that can contain several types of Outlook data:

• Emails — Every message you have sent, received, or drafted, including attachments and inline images.
• Contacts — Your address book entries with names, phone numbers, email addresses, and notes.
• Calendar events — Meetings, appointments, and recurring events with all their metadata.
• Tasks — To-do items with due dates, priorities, and status tracking.
• Notes — Quick notes created within Outlook.
• Folder structure — The entire hierarchy of folders and subfolders you have organized your mail into.

All of this data is stored in a single file, which makes PST files both convenient for backups and challenging when they grow very large.

Common Scenarios Where You Encounter PST Files

You might need to deal with PST files in a number of situations:

Corporate Email Archives

Many organizations export employee mailboxes to PST files when employees leave the company or when migrating to a new email platform. These archives often need to be accessed months or years later.

Leaving Outlook

If you are switching from Outlook to another email client — whether on Mac, Linux, or a web-based platform — you will need to export your mailbox as a PST file and then convert it to a compatible format. Mac users can follow our guide to open PST files on Mac without Outlook.

Legal Discovery and Compliance

In legal proceedings, email archives are frequently requested as evidence. PST files are the standard export format from Outlook environments, and legal teams often need to search, review, or convert them. If your organization operates under European regulations, our guide on GDPR and email archiving covers the compliance requirements.

Backups and Migration

System administrators regularly create PST backups of user mailboxes before server migrations, upgrades, or decommissioning. These backups may later need to be restored or converted.

How to Open PST Files

On Windows with Outlook

The most straightforward way to open a PST file is with Microsoft Outlook on Windows. You can go to File > Open & Export > Open Outlook Data File and select your PST file. Outlook will mount it as a separate mailbox in your folder pane.

This method works well but requires a paid Outlook license and only runs on Windows.

On Mac

Outlook for Mac has historically offered limited PST support. Newer versions can import PST files, but the process can be slow and sometimes fails with large or complex archives. Certain data types like custom forms or specific calendar metadata may not transfer correctly.

On Linux

There is no native support for PST files on Linux. While some open-source command-line tools exist to parse PST data, they often struggle with large files, lack a visual interface, and may not extract all content types reliably.

How to Open PST Files Without Outlook

The simplest way to open and read a PST file without installing any software is to use MailtoPst, the only cloud-based email converter available online.

Here is how it works:

1. Upload your PST file directly from your browser — no software installation required.
2. Preview your emails, folder structure, and attachments right in the web interface.
3. Convert to the format you need, or simply browse and read your archived emails.

Because MailtoPst runs entirely in the cloud, it works on any operating system — Windows, Mac, Linux, or even a tablet. There is nothing to download or configure.

Supported Conversion Formats

Once your PST file is uploaded to MailtoPst, you can convert it to several widely used email formats:

• MBOX — The universal mailbox format supported by Thunderbird, Apple Mail, and many other clients. See our guide on converting PST to MBOX without Outlook.
• EML — Individual email files that can be opened by virtually any email application.
• MSG — Single-message files compatible with the Outlook ecosystem.
• EMLX — The native format for Apple Mail on macOS.

This flexibility means you can move your email data to practically any platform without losing messages, attachments, or folder organization.

PST File Size Limits and Best Practices

PST files can theoretically grow up to 50 GB in modern versions of Outlook (Unicode format). Older ANSI-format PST files had a much stricter limit of around 2 GB, and exceeding that limit often caused data corruption.

Even with the higher modern limit, working with very large PST files can be problematic:

• Performance degrades as the file grows beyond 10-20 GB. Outlook may become sluggish or unresponsive.
• Corruption risk increases with larger files, especially if the application crashes during a write operation.
• Backup and transfer times grow proportionally with file size.

Best practices include splitting large mailboxes into multiple smaller PST files organized by year or department, and running the built-in repair tool (scanpst.exe) periodically on important archives.

Security Considerations

PST files support password protection, but it is important to understand its limitations. The password mechanism in PST files is relatively weak and primarily prevents casual access — it is not equivalent to strong encryption. Sensitive PST archives should be stored on encrypted drives or within secure storage systems.

When uploading PST files to any online service, make sure the platform uses encrypted connections (HTTPS) and does not retain your data longer than necessary. MailtoPst processes your files securely and does not store your email data after conversion is complete.

Start Working with Your PST Files Today

Whether you need to read old email archives, migrate to a new platform, or convert PST files for legal review, MailtoPst makes it simple. As the only cloud-based email converter, it lets you upload, preview, and convert your PST files from any browser — no Outlook license required, no software to install.

Visit MailtoPst to get started with your first conversion.