Free Online PST Viewer
Open an Outlook PST file in your browser. The whole folder tree, with mail, contacts and calendar sitting together as Outlook kept them.
Mailbox tooling from OnlinePCApps since 2013
When Nothing Will Open Your PST File
Almost everyone lands here for one of three reasons. All three finish with the folder tree on screen.
Outlook Is Not on This Machine
A PST arrived from a colleague, a leaver or an old backup drive, and the only program that opens it is a licence you do not have.
Outlook Refuses to Mount It
The file opens nowhere and Outlook offers only an error. Nine times out of ten it is an older archive that has run into a size ceiling nobody warned about.
The File Is Too Sensitive to Upload
A legal hold, a payroll mailbox, a board thread. Handing the whole database to a stranger's server to read one message is not proportionate.
Open a PST File in 3 Steps
Select the Mailbox File
Drag the .pst onto the panel or pick it from disk. The database is read in place, which is why no upload bar appears.
Walk the Folder Tree
The tree arrives exactly as Outlook left it. Pick a folder to list what is in it, then pick an item to see its body, its properties or what is attached.
Take What You Need
Grab an attachment, write a single item out as EML, or push it to your printer as PDF. None of those are gated.
This PST Viewer vs The Alternatives
Almost every PST viewer is a Windows download, and the free tiers tend to stop at the point you want to keep something.
| What matters | This page This viewer Runs in your browser | A typical Windows PST viewer Installs and may gate features |
|---|---|---|
| Where the database is processed | Never | On their server |
| Saving an attachment | None | Commonly 500 MB |
| Exporting an item | No | Commonly a paid feature |
| Copying text out | Under a second | A download and a setup wizard |
| Operating system | $0 | Commonly a paid feature |
| Install required | Never, it is local | Sometimes gated too |
| Mailbox leaves your control | Never | No |
| Mailbox leaves your control | Not applicable | For the length of the session |
That describes the category as a whole and not any single named product.
Your PST File Never Reaches Our Servers
A rival PST viewer warns, correctly, against handing a mail database to an online converter. The warning is sound. The answer is not to be one.
No endpoint here can accept a mailbox, and no server-side component sits behind this app at all. Put the network panel on screen and load a file to see it for yourself. The store is opened read only into the bargain, so nothing about it shifts.
→ external requests ....... 0
→ your mailbox ....... 0 requests
What a PST File Actually Holds
A PST is not a folder of messages. It is a small database with its own node layer, its own property store and its own size ceilings, and knowing that explains most of the trouble people have with one.
| Part | Header | What it holds |
|---|---|---|
| Node database | NDB layer | The bottom layer. A B-tree of nodes and blocks, closer to a small database file than to a mail folder. |
| Property store | PC and TC | Property contexts and table contexts sit above the nodes. Every item is a bag of numbered properties rather than named headers. |
| ANSI variant | Outlook 97 to 2002 | Uses 32-bit internal pointers and stops hard at 2 GB. Most PST files that refuse to open have simply hit this ceiling. |
| Unicode variant | Outlook 2003 onward | 64-bit pointers, a default ceiling near 50 GB, and the only variant Outlook has created for two decades. |
| Folder hierarchy | IPM Subtree | The tree Outlook shows you. Deleted Items, Search Folders and the root all live here as ordinary nodes. |
| Message items | IPM.Note | Mail. Sender, recipients, body and attachments held as properties rather than as an RFC 5322 header block. |
| Non-mail items | IPM.Contact, IPM.Appointment, IPM.Task | Contacts, calendar entries, tasks, notes and journals share the same store. A PST is a mailbox, not a mail file. |
| Attachments | attachment table | Kept as separate nodes and referenced by the message, which is why a PST grows faster than the mail inside it. |
| Encryption | compressible or high | Outlook can obfuscate the file with a simple permutation. It is not real encryption and does not stop a reader. |
| Password | PST password property | Stored as a CRC of the password, not the password. It gates Outlook and nothing else. |
| Deleted items | recoverable nodes | Removing an item unlinks it from the tree without clearing the node, which is why deleted mail often still resolves. |
Documentation behind the format
PST is a Microsoft format, but it is not a secret one. Microsoft publishes the structure itself, which is what allows a reader written by anybody else to walk the same tree Outlook walks. The documents below are the ones this app is built against.
Property numbers absent from MS-OXPROPS, are named properties, allocated inside one mailbox rather than fixed globally. Those resolve here too.
Other Ways to Open a PST File
There are four other routes into a PST. Each one works, and each one asks for something in return.
Use Outlook Itself
Run scanpst.exe
Convert It First
Mount It on a Server
Check the Variant First
Look at pst.exe and 2 GB sits at a fixed offset in the header and tells you whether the file is ANSI or Unicode. An ANSI PST that has reached its ceiling explains most refusals to open.
Ask Outlook Where It Filed It
Look at Account Settings and Data Files is the tab that lists every store Outlook knows about along with its full path. Faster than guessing at Documents or AppData.
When a PST Outgrows the Tab
There is a ceiling on what one tab can hold. The desktop build covers the stores that sit above it.
What the Desktop Build Is For
The browser holds the database in memory while it resolves the tree. A departmental archive is fine. A 50 GB Unicode store from a long-serving mailbox is not, and a phone gives up far sooner than a laptop does.
Reading from disk in pieces is what the desktop build does instead, which takes store size off the table.
Never reaches out once installed. Suited to isolated estates and to networks that block outbound traffic at the edge.
A 50 GB Unicode PST streams from disk instead of being held in RAM, so size stops mattering.
Find an item across the whole tree by sender, subject, date or body, not just inside the folder you have open.
Several mailboxes queued together, past the ceiling a single tab can hold.
Turn an entire store into PST, MBOX, EML or PDF in one pass with properties preserved.
No connection needed after install, which suits restricted estates and air gapped machines.
Questions About Reading PST Files
Other Mailbox & File Apps
Each of these runs on the same principle: your machine does the work.
Who Built This PST Reader
That PST Nobody Can Open
Drop it in and the tree appears. No install, no sign-up, and the file stays where it is.