What is a PST file?

A PST file (Personal Storage Table, shown in Outlook as an Outlook Data File) is a database that holds an entire mailbox: mail folders, contacts, calendar, tasks and the attachments inside the messages. This page explains who creates PST files, how they are organized, how to create, open and move one, and what to do when you need the emails as PDF. A browser cannot read a PST, so to use SaveMail you first save single messages out of Outlook as .msg files.

PST file: definition and what .pst stands for

PST stands for Personal Storage Table. It is the file Microsoft Outlook uses to keep a mailbox on your own disk rather than on a mail server. One .pst file contains a tree of folders (Inbox, Sent Items, your own subfolders) and every item in them: emails with their attachments, contacts, calendar entries, tasks and notes.

Outlook creates PST files in three cases. For POP accounts, the PST is the mailbox itself. For Archive, AutoArchive or manual archiving moves old items out of the main mailbox into a PST. For Export, you choose File, Open & Export, Import/Export, Export to a file, Outlook Data File. Exchange and Microsoft 365 accounts use a cached copy called OST instead, which has the same structure but is tied to the account and not meant to be moved.

Gmail, Apple Mail and Thunderbird do not read or write PST. Their mailbox format is MBOX.

Have the email as a file (EML, MSG, MBOX)? Convert it to PDF in your browser: nothing is uploaded.

How a PST file is structured

A PST is a database, not a collection of messages. Inside, Outlook keeps a B-tree index of nodes and blocks: a folder is a node, a message is a node, and attachments are sub-nodes of the message. Properties (subject, sender, body, received time) sit in property tables keyed by MAPI identifiers, the same system the single-message MSG format uses. Data blocks may be lightly scrambled by a reversible encoding setting that is not real encryption.

Two generations exist. ANSI PST files from Outlook 97 to 2002 are capped at 2 GB and break if they grow past it. Unicode PST files, used since Outlook 2003, support international text and are limited by a configurable size, 50 GB by default in current versions. Microsoft documents the format, but the database structure is why ordinary tools, and browsers, cannot simply open it.

Does a PST file contain attachments? Yes, every attachment of every message is stored inside. Does it contain contacts? Yes, if the Contacts folder was included in the export or archive.

How to create a PST file

The two common routes in classic Outlook for Windows:

1. Export a copy of the mailbox: File, Open & Export, Import/Export, Export to a file, Outlook Data File (.pst), choose the account or folder, tick Include subfolders, pick a location, Finish. A password is optional.
2. Add an empty data file to work with: File, Account Settings, Account Settings, Data Files tab, Add, name the file. The new PST appears in the folder pane and you can drag messages into it.

The new Outlook for Windows and Outlook on the web do not create PST files; use classic Outlook, or for a Microsoft 365 mailbox ask the administrator for an export. The Gmail equivalent is a Takeout MBOX, and moving between the two is covered in Gmail to PST and PST to Gmail.

How to open a PST file

Open it in classic Outlook: File, Open & Export, Open Outlook Data File, select the .pst, and it appears as a separate top-level folder in the folder pane. Right-click it and choose Close when you are done. Importing (File, Open & Export, Import/Export, Import from another program or file) copies the items into your mailbox instead of opening them side by side.

Without Outlook, a free PST viewer for Windows can display folders and messages read-only, and open-source command-line tools exist for macOS and Linux. The full set of options, including the new Outlook and finding a lost PST, is in how to open a PST file.

Why a browser cannot read a PST, and how to get PDFs from it

SaveMail opens EML, MSG and MBOX because each is either plain text or a small, self-contained container that JavaScript can parse in memory. A PST is a multi-gigabyte database with its own indexes and block encoding; reading it reliably requires a full database driver, and a browser tab is the wrong place for that. That is why PST and OST are listed as not supported, and there is no upload that could send them to a server either.

To get a PDF of PST emails:

1. Open the PST in Outlook as described above.
2. Select the messages you need and drag them to a folder on the desktop; each becomes an .msg file.
3. Drop the MSG files into SaveMail one at a time, read them in the browser, and press Save as PDF; attachments can be downloaded next to the PDF.

Nothing is uploaded at step 3, which matters when the PST holds client or HR correspondence. For a few messages, Outlook's own File, Print, Microsoft Print to PDF also works but leaves attachments behind; all the paths are compared in PST to PDF.

PST vs EML vs MSG vs MBOX

A note on the danger of PST files: they corrupt more easily than server mailboxes when they grow large or are copied while Outlook has them open, the password is weak protection, and they walk out of a company on a flash drive without effort. Keep a backup and treat a PST as sensitive data.

Frequently asked questions