OST to PST Converter Software for Windows: Free Download

How to Convert an OST File to PST

1. Add your OST file

Drag the .ost into the window, or click Add File. You do not need the matching Outlook profile. Point the app straight at the orphaned cache, wherever you copied it from.

2. Choose PST output

Set the output to PST. The folder tree from the source is kept as is, so Inbox and Sent and every subfolder land in the same place inside the new archive.

3. Start the conversion

Click Start. The app reads through the whole OST, writes a valid Unicode PST, and leaves the original .ost untouched. Open the result in Outlook with File, Open, Outlook Data File.

What the converter does

Opens an orphaned OST

The reader opens a .ost with no Outlook running and no Exchange behind it, including a file whose MAPI profile was deleted. That is the case Outlook itself cannot handle, since it has no way to import an .ost.

Rebuilds the real folder tree

The output is a Unicode PST with the same hierarchy as the source, Inbox, Sent, Archive, and nested subfolders, not a flat pile of loose messages. Empty system folders like Search Root are trimmed out.

Keeps each message byte-exact

Subject, HTML and plain-text body, sender, dates, the read or unread flag, and attachments all carry over unchanged, so the archive reads the way the mailbox did.

Pick only the folders you need

The window shows the OST as a tree with checkboxes. Convert the whole store, or tick a single folder. Handy when you only want one project's mail out of a 6 GB cache.

A PST any Outlook opens

The result is a standard Outlook Data File that opens in Outlook 2016 and later. The source can be an OST cached from an Exchange or Microsoft 365 account, the converter does not care which server it came from.

Who uses OST to PST Converter

IT admins and help desks

A machine comes in with a leftover .ost and no working profile: maybe a departed employee, maybe a rebuilt PC whose Exchange cache got disconnected. You pull the mail into a PST for the record, and no need to stand the old account back up.

People who lost Exchange access

You left a job or the account was disabled, and the only copy of years of mail is the cached OST on your laptop. The server side is gone, but the file still has everything in it.

Anyone with an orphaned .ost

An old drive, a backup folder, a file Outlook now refuses to touch. Point the converter at it and save the parts that matter, with no account to recover first.

OST vs PST: what the converter changes

The two files look similar, but Outlook treats them very differently. That gap is the whole reason this tool exists.

File	What it is	Can Outlook open it?
OST	.ost, an offline cache of an Exchange or Microsoft 365 mailbox, tied to one MAPI profile	No. Outlook imports PST, and there is no menu to import an .ost
Orphaned OST	An .ost whose profile or account was deleted, so it can no longer be reattached to Outlook	Not without converting it first
PST	.pst, a portable Outlook archive that carries the full folder tree	Yes. File, Open, Outlook Data File

Download for Free

OST to PST Converter Tool

Languages

File Size

9 Mb

Version

1.0

Last updated on

22/05/26

$ 19.99

🖥️ System Requirements

Windows 11/10/8.1/8/7 (32/64 bit)
Intel i3, AMD Ryzen 5 or above
4 GB of RAM or above
NVIDIA® GeForce® series 8 and 8M, Intel® HD Graphics 2000, Quadro FX 4800, Quadro FX 5600, AMD Radeon™ R600, Mobility Radeon™ HD 4330, Mobility FirePro™ series, Radeon™ R5 M230 or higher graphics card with up-to-date drivers
1280 × 768 screen resolution, 32-bit color
1 GB of free hard disk space or above

🙋 Frequently Asked Questions

❓ Can I open an OST file without Outlook?

Yes. The converter reads the .ost directly with its own engine, so Outlook does not have to be installed or running. You get a .pst you can then open in any Outlook, or keep as an archive.

❓ Is an OST file the same as a PST?

No. An OST is an offline copy of a mailbox that lives on a server, kept in sync while you are connected and tied to one Outlook profile. A PST is a self-contained archive you own outright. The converter turns the first into the second.

❓ How do I convert OST to PST without Outlook installed?

Add the .ost, choose PST as the output, and start. Reading the file and writing the PST both happen inside this app, not through Outlook, so a PC with no Office at all still does the job.

❓ What is an orphaned OST, and can I still read it?

An orphaned OST is a cache whose Outlook profile or Exchange account has been removed, so Outlook can no longer reattach it. The file itself still holds the mail. This tool reads that file and writes the messages into a PST you can open.

❓ Can I open an old .ost file in Outlook directly?

Short answer: no. Long answer: Outlook has an import path for PST only, and even a matching account will not mount an old, disconnected .ost. Converting it to PST is the supported way to get the contents back.

❓ Why can't I just open the OST file I have?

Because an .ost is bound to the profile and Exchange account that created it. Move it to another PC or delete that profile, and Outlook sees a file it will not touch. The bytes are fine, the link to the account is what is missing, and that is what conversion works around.

❓ Will it run on Windows 11?

Yes, it runs on Windows 10 and 11. There is no Mac build. The free download is a normal Windows installer, and it needs neither Outlook nor an Exchange connection to convert a file.

❓ Is my mailbox uploaded anywhere?

Short answer: no. Long answer: the whole conversion runs on your machine, which is the reason admins handling a confidential mailbox pick a desktop tool over a web converter that asks you to upload the entire .ost first.