How to open a PST or OST file without Outlook

PST and OST: what the two files are

• .pst, an Outlook Data File. It holds Outlook messages and other Outlook items. Microsoft says that with a POP or IMAP account, all your Outlook information is stored in such a file, and that an Exchange account can have one from AutoArchive. A .pst can be copied to a new computer and opened there.
• .ost, an offline Outlook Data File. Microsoft calls it a copy of items saved on a mail server. Outlook creates it when you add an account that uses one, and downloads the data from the server into it. Microsoft says it does not need to be backed up like a .pst.

Why an .ost from another PC is different

Microsoft's page Find and transfer Outlook data files from one computer to another is clear about it. For Microsoft 365, Exchange and Outlook.com accounts, Outlook re-creates the .ost when you add the account, and you cannot move that file from one computer to another. The mail of these accounts is backed up on the mail server.

So while the mailbox is still on the server, setting the account up again is the simple route: Outlook downloads the mail into a new .ost. When the mailbox is gone, for example after a former employee's account was closed, the old .ost holds the copy that was made on that PC, and the Microsoft pages we checked give no way to open it in Outlook.

Option 1: classic Outlook, for .pst files

To look inside a .pst without copying anything into your mailbox (Microsoft's steps):

1. In classic Outlook, choose File, Open & Export, Open Outlook Data File.
2. Choose the .pst file.
3. Expand it in the Navigation pane to see its folders.

To copy the items into your mailbox instead, choose File, Open & Export, Import/Export, then Import from another program or file, then Outlook Data File (.pst). The wizard asks for the password if the file has one and lets you choose where the items go (Microsoft's import steps).

Good: nothing extra to buy if classic Outlook is already on the PC, and you see the items as Outlook shows them. Less good: you need classic Outlook installed, and these steps are for .pst files, not for an .ost from another PC.

Option 2: new Outlook for Windows, with conditions

Microsoft's pages say new Outlook for Windows can open a .pst file, read and search the e-mails in it, and move, copy or delete e-mails and folders. To open one, go to Settings, then Data files, select Outlook Data Files, then Add file, choose the .pst and select Open. Microsoft's import page also describes an Import option there, which copies selected items into a mailbox.

Microsoft lists these conditions:

• classic Outlook must be installed as well, with the same architecture (32-bit or 64-bit) as new Outlook;
• the account you use in new Outlook needs a Microsoft 365 subscription;
• the ARM version of new Outlook does not support Outlook Data Files;
• new Outlook must not be running in Safe or Recovery mode.

So new Outlook is no way round classic Outlook: it needs classic Outlook on the same PC. Microsoft's pages describe this for .pst files, not for .ost files.

Option 3: Inboxwright ($9.99)

Inboxwright is a Windows app from Karelia Labs that opens Outlook .pst and .ost files on a PC that has no Outlook. It works offline and only reads the data file; it never changes it. Get it from Microsoft Store.

1. If Outlook is using the file, close Outlook first.
2. Start Inboxwright and press Ctrl+O, or drop the .pst or .ost file on the window.
3. Choose a folder in the tree. Every folder shows how many items it holds, system folders included.

Messages open in a three-pane window: folders, message list and reading pane. HTML, rich text and plain text messages are shown as they were sent, with the pictures that were sent inside them. Content from the internet is always blocked: tracking pixels, remote pictures, styles and scripts are removed before a message is shown, and Inboxwright tells you when something was blocked.

Attachments can be opened, or saved one by one or all at once. Attached messages open in their own window or can be saved as .eml files. Programs and scripts attached to mail are never opened, only saved. Search covers words, sender, recipient, date range and attachments, in one folder, a folder and its subfolders, or the whole file.

Export the selected messages, a folder, a folder with its subfolders, the search results or everything:

• messages as EML files with their attachments and original internet headers, as MBOX (one file per folder), as PDF files or as HTML pages that work offline;
• only the attachments;
• contacts as vCard (.vcf) or CSV;
• calendar items as iCalendar (.ics) or CSV.

Exports keep the folder structure of the data file and never overwrite existing files. You can skip duplicates (the same message in more than one folder) and limit an export to a date range or a sender. Each export can be cancelled and ends with a summary and a report next to the files. The file summary shows how many messages, folders, contacts and calendar items a file holds, the date range of the mail, the biggest folders, the top senders and messages per year. Try a sample opens a made-up sample mailbox, so you can see the app work first.

Inboxwright also scans the file's own index, so a message whose folder list is damaged still appears, marked as found by scanning. Damaged, incomplete or wrong files get a clear message, and one damaged item does not stop the rest of the file from opening.

Which route fits

A converter website means uploading the whole mailbox. Think twice with personal or work mail.

What to expect from Inboxwright

• Tested file kinds: .pst files in the Outlook 97–2002 (ANSI) format and the Outlook 2003 and later (Unicode) format, .ost files from Outlook 2013 and later, including outlook.com accounts, and .pst files with a password set in Outlook.
• Encrypted mail: messages encrypted with S/MIME cannot be read without the recipient's certificate.
• Close Outlook first before you open a file that Outlook is using.
• Large .ost folders are slower to list. For .ost files, Inboxwright reads each row of a folder's message list from the message itself, which takes longer in very large folders.
• WebView2: showing messages and making PDF files need the Microsoft Edge WebView2 Runtime. It is part of Windows 11, and Microsoft says the vast majority of Windows 10 PCs already have it (Microsoft Learn).
• It does not write .pst files. Inboxwright reads .pst and .ost files but does not write them, so it does not turn an .ost into a .pst for Outlook. Its exports are EML, MBOX, PDF, HTML, vCard, CSV and ICS files.
• Windows only: Windows 10 version 2004 or later, or Windows 11, 64-bit (x64), with free disk space for the exported files. Outlook is not needed.

Microsoft's steps and conditions are from the four Microsoft support pages linked above, and the WebView2 note is from Microsoft Learn, all checked on 15 November 2026. Inboxwright's results are based on our tests with eight public test files from open-source PST projects; on all eight, its folder, item and attachment counts agreed with those of a second, independent reader. The sample mailbox is made up.