Guides / Open a PST without Outlook
How to open a PST file without Outlook
Updated August 30, 2026
Somebody handed you a .pst file. It is the mailbox of a person who left, or an archive from an old machine, or the thing IT produced when you asked for “all the emails from that project”. You do not have Outlook, and buying a licence to read one file is an absurd way to spend a morning.
What a PST actually is
A PST is a whole mailbox in one file: a small database holding folders, messages, attachments, contacts and calendar items. That is why nothing else opens it by double-clicking. It is not a document, it is a database in a format Microsoft built for Outlook.
An .ost is the near relative: the offline cache of a mailbox that lives on a server. Same idea, but it is bound to the profile that created it, which matters below.
First, ask whether you need the file at all
If the PST came from a Microsoft 365, Exchange or IMAP account that still exists, the mail is probably still on the server. Adding that account to any mail client gets you everything, searchable, in a couple of minutes, and the PST becomes a backup you never have to open. People spend hours converting an archive of mail they already have. Check first.
The routes that work
- Any Outlook you can borrow. Old versions count. File, then Open and Export, then Open Outlook Data File. The folders appear in the sidebar and you can drag messages out. If a colleague has Outlook and ten minutes, this is the shortest path in existence.
- readpst, on the command line. Part of the libpst project, free and open source. Install it with brew install libpst on macOS or your distribution's pst-utils package, then run readpst -o exported archive.pst. It writes the mailbox out as standard mbox files, one per folder, and it handles enormous archives without complaint. Run readpst -h for the other output modes, including one file per message. The libpff project's pffexport does a similar job if readpst chokes.
- Then read the mbox in a normal client. Thunderbird with the ImportExportTools NG add-on imports mbox directly, and it is free on every platform. Apple Mail imports mbox from its File menu. Either gives you a searchable mailbox with attachments intact.
- Open it in your browser. If a command line is not your world, FileQuiet's email archive tool reads PST and OST files in the tab, with nothing uploaded. Browsing, reading and searching are free.
What does not work: Thunderbird cannot read a PST directly, no matter how you rename it, and neither can Apple Mail. Outlook for Mac has offered PST import in some releases and not others, so check the File menu of the version in front of you rather than a blog post about a different one.
The .ost complication
An OST cannot simply be attached to a fresh Outlook profile the way a PST can, because it is tied to the account that built it. If that mailbox still exists on the server, re-syncing the account is the clean answer and gives you a working mailbox instead of a frozen copy. If the account is gone and the OST is all that survives, you need a tool that reads the raw format: readpst handles OST files, and so does the browser tool above.
If it asks for a password
A PST can carry a password that Outlook asks for on open. If you have the password and access to Outlook, remove it there first: File, Account Settings, Data Files, select the file, then Settings. Working with an unprotected copy saves an argument with every other tool afterwards. FileQuiet will not open a password-protected PST and says so rather than guessing.
Size is the thing that bites
PST files grow to tens of gigabytes, and how you open one depends on which side of a few gigabytes it sits. Command line tools stream from disk and do not care. Anything that loads the archive into memory, including a browser tab, has a ceiling. If your file is very large, use readpst, or export one folder at a time.
If you just need to read it and pull a few messages
FileQuiet's email archive tool opens PST, OST, OLM and MBOX files inside your browser tab. Nothing is uploaded: the parser is JavaScript running on your machine, and you can watch the network tab to confirm it. Opening, browsing, searching and saving a single message as .eml or PDF are free. Bulk export of the whole archive to PDF, individual .eml files or a CSV index is a one-time $12.
Open an email archive in your browserHonest limits: the archive is held in your browser's memory, so a very large PST needs readpst instead. Password-protected files are refused rather than cracked.
Frequently asked
Can Thunderbird open a PST file?
Not directly, and there is no add-on that changes that reliably. The working path is to convert the PST to mbox with readpst first, then import the mbox into Thunderbird with ImportExportTools NG. Both halves are free.
What is the difference between a PST and an OST file?
A PST is a standalone mailbox file you can move between machines and attach to any Outlook profile. An OST is a local cache of a mailbox that lives on a server, tied to the profile that created it, which is why Outlook will not simply mount one. If the server mailbox still exists, re-syncing beats converting the OST.
Are free online PST viewers safe?
Read what they do with the file. Most of them work by uploading your mailbox to their server, and a mailbox is the single most revealing file most people own: it holds password resets, contracts, medical appointments and every private conversation you have had at work. If the tool does not say plainly where the parsing happens, assume it happens on their machine.
Can I get just the attachments out of a PST?
Yes. readpst writes attachments alongside the messages it exports, so a converted archive gives you a folder tree you can search with your file manager. In a viewer, opening the message and saving the attachment works for a handful. For hundreds, convert on the command line.