Corbett

OST Converter

Corbett OST Converter opens Outlook OST files on Windows, including orphaned ones that Outlook refuses, and saves mail as PST, EML, MBOX, PDF, HTML, TXT or CSV. Folders, dates and attachments stay intact, and Outlook does not need to be installed. Try free demo first.

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4.6 out of 5 from 683 reviews

Works offline on your PC. Corbett never sees your OST file or messages.

Free demo, scanned clean on VirusTotal and a 30-day money-back window.

Lifetime licence from $99 Demo converts 10 emails per folder

Quick answer

What Is an OST Converter?

An OST converter opens an Outlook OST file and saves its emails and attachments in another format. Corbett OST Converter does that offline on Windows, so an OST from a deleted profile or a closed server opens in Outlook, Thunderbird or a PDF viewer.

What it opens

Single, many, large and orphaned OST files

What it saves

PST, EML, MBOX, PDF, HTML, TXT, CSV and more

Who uses it

Admins, users after a migration, lawyers and switchers

Conversion scope

OST Converter for Outlook Offline Data

OST Converter Unlocks Mail Outlook Will Not Open

Outlook keeps a cached copy of an Exchange, Microsoft 365 or IMAP mailbox in an OST file. Once the profile is gone or the server shuts down, Outlook refuses that file and the mail inside stays out of reach. OST converter loads the file alone and saves your mail in formats any program accepts.

Kept in output

Folder tree
Attachments
Message dates
Full headers
Unread status

OST input types

Orphaned OST files
Inaccessible OST files
Exchange and Microsoft 365 cache files
Large OST files
Many OST files at once

Outputs

PST
EML
MBOX
PDF
HTML
TXT
CSV

Not needed

Outlook install
Exchange connection
Internet connection
Mailbox password

Outlook cannot import from an OST file

Microsoft overview of Outlook Data Files says OST files hold a synced local copy of your mailbox and that you cannot import from an .ost file or move its contents into another profile. OST converter reads the file on its own, so that limit does not apply.

Import OST file into Outlook

Related pages: PST Converter, MBOX Converter, OLM Converter and MSG Converter. Other mail files sit on email converter tool page.

Core features

OST Converter Features by Screen

Five screens of Corbett OST converter software, in conversion order.

OST converter email data files list with Outlook OST files option

Source files

Open Your OST File

Select Open, then Email Data Files, and choose Outlook OST Files. OST file converter loads your file into its panel, and no Outlook or Exchange link is needed.

A spare PC with no Outlook still works. OST file converter reads your file and leaves it as it was.

OST converter choose from a folder option

Batch loading

Choose Files or Choose From a Folder

Select a single OST file, or choose a folder to load several OST files in one step.

Loaded files appear in one tree, so OST converter handles many OST files, large ones included, in a single session. No file size limit applies.

OST converter email preview with content, header, properties, hex and raw views

Message preview

Preview OST Emails Before Converting

Click any message and a reading pane opens beside five analysis views. Admins use them to confirm correct folders before an export starts.

Content shows the email body. Message header lists routing details such as sender, recipient and date. Properties reports item attributes, while hex and raw message views show stored values and code.

OST converter export menu with email file and document formats

Output formats

Select Your Output Format

Email files export to PST, EML or MBOX. Document files export to PDF, HTML, TXT or CSV. The Export menu also lists Gmail, Office 365, IMAP and Thunderbird for sending mail into an account.

Search by keyword first, then save only matched items. Quick search highlights hits in yellow, and Advance search checks every field or only name, subject, To, Cc and content.

Export options

Set OST Export Options Before You Save

Switch on open folder after export, skip greyed out folders, create empty folders and include email headers. For PST output, create an individual PST file for every folder, so small files stay healthy.

Select Browse to choose a destination, then Save. Live progress shows every folder as it converts. Need Outlook files? Open OST to PST Converter.

Working process

How to Convert an OST File in Four Steps

Four steps take an OST file to its new format. Try them on one file in free demo first.

Open your OST file

Start OST converter, select Open, then Email Data Files and choose Outlook OST Files. Select a file or choose a folder to load many.

Preview and select folders

Your OST loads as one folder tree. Click any email to preview it, tick folders and search by keyword to trim your conversion.

Choose your output

Select Export and choose a format: PST, EML or MBOX for email files, PDF, HTML, TXT or CSV for documents.

Save your converted mail

Set options, select Browse for a folder and press Save. Live progress shows every folder, and Open Folder takes you to your output.

Want screenshots for every click? Follow OST converter guide.

Working process

OST Converter Video Walkthrough

Prefer text? Open Import OST file into Outlook to see how Outlook handles an OST file.

Advanced options

More OST Converter Features for Big Jobs

Small options that save hours when you convert OST files in bulk.

Batch OST conversion

Many OST files converted in one session

No file size limit

Large OST files convert too with OST converter

Folder hierarchy kept

Inbox, Sent and subfolders stay in order

Attachment extraction

Save attachments alone from any OST

Email address extraction

Export addresses to CSV

Phone number extraction

Pull numbers from message bodies

File naming options

Name output by From, To, Date or Subject

Smart filters

Date, sender, subject and size

Quick and advance search

Find emails before you convert

Five preview views

Content, header, properties, hex and raw message

Individual PST per folder

One PST file for every folder

Log and CSV report

See what converted and what failed

USB and NAS targets

Save output to external drives and network storage

Include email headers

Keep full header data in output

Orphaned file support

Open OST files with no profile or server

Choose output

OST Converter Output Formats

OST converter saves to nine file formats. Match format to where your converted mail will open.

Format	Best for	Opens in
PST	One file per mailbox with folders intact	Microsoft Outlook
MBOX	Moving mail to a free email client	Thunderbird and Apple Mail
EML	One file per email, easy to search	Windows Mail and most email clients
PDF	Legal files, audits and printing	Any PDF viewer
HTML	Reading mail with no email client	Any web browser
TXT	Plain text archives	Any text editor
CSV	Lists of senders, dates and subjects	Excel and Google Sheets
vCard	Contacts moved into a phone or address book	Outlook, Gmail and phones
ICS	Calendar entries shared between apps	Outlook, Google Calendar and Apple Calendar

Free demo

Test OST Converter on a Real OST

Install free demo, open an OST file, select a folder and choose a format. Free demo converts 10 emails per folder, so your output is quick to check.

Download free demo

Try before you buy

Free Demo vs Full OST Converter

Free demo opens, previews and searches your full OST. Only conversion is capped.

Feature	Free demo	Full version
Open OST and load folders	Yes	Yes
Preview, search and analysis views	All available	All available
Emails converted per folder	10	Unlimited
OST size and file count	Conversion stops at 10 per folder	No limit
Price	Free	From $99 one time

Use cases

Who Needs an OST Converter?

Anyone who must convert an OST file that Outlook will not open.

Users after a profile reset

OST converter saves mail from an old profile as PST and keeps folders in place.

Teams after a server shutdown

OST converter saves files left by a closed Exchange or hosted server and keeps years of mail.

Legal and compliance teams

Convert OST emails to PDF with OST converter and name sender, date and attachments named clearly for case files and audits.

IT admins after a switch

OST converter saves leftover OST files from retired PCs in formats users open without the old profile.

Investigators

Preview message header, hex and raw views for an OST of unknown origin before you export.

Marketers and list builders

Export addresses and phone numbers from an old OST to CSV for outreach.

Why Corbett

Why Choose Corbett OST Converter?

No subscription

Lifetime price from $99

Works offline

No sign-in and no upload

Original stays safe

OST opens read only

No Outlook needed

Convert OST with no Outlook

No size limit

Any OST size and file count

Folders kept

Hierarchy stays in order

Smart filters

Date, sender, subject and size

30-day refund

Money-back window after purchase

Before conversion

OST Converter Scope and Limits

OST converter turns an Outlook offline file into another format. Here is what that covers and where it stops.

Capability	Supported	What it means
File to file conversion	Yes	OST to PST, EML, MBOX, PDF, HTML, TXT and CSV with folders kept
Orphaned OST	Yes	Files from deleted profiles and closed servers open on their own
Outlook installed	Not needed	Files open on a PC with no Outlook
Source OST	Read only	Output goes to a new folder and your original stays as it was
Internet and passwords	Not needed	Conversion works offline on local files
Profile settings and rules	Not converted	Account settings, server rules and autocomplete stay behind
Live mailboxes	Other mode	Use Email Backup Software or Email Migration Tool for accounts
Mac and Linux	No	OST converter installs on Windows only

Outlook or tool

OST Converter vs Outlook Export

Outlook exports a live account to a PST file, but Microsoft overview of Outlook Data Files says you cannot import from an .ost file. Here is where Outlook stops.

Task	Outlook export	OST Converter
Cost	Free	From $99 one time
A handful of emails	Works from a live profile	Works too
Orphaned OST	Cannot open your file	Opens and converts
OST to another profile	Import from OST not supported	Saves to PST, EML or MBOX first
Many OST files	One profile at a time	One batch of files or folders
Filters	Basic search only	Date, time, To, From, size and name
PDF file names	Typed in by hand	Named by From, To, Date or Subject
Machine without Outlook	Cannot open your file	Opens files by itself

Outlook export wins for a handful of messages from a working profile.

Global recognition

OST Converter Software Users Trust

Users rate Corbett OST converter 4.6 out of 5 from 683 reviews, and these software directories list it.

CNET
Download.io
UpdateStar
TopSoftware Advisor
SaaSHub
Uptodown

Specifications

OST Converter Specifications

Download details

Download size: 87.4 MB
Demo limit: 10 items per folder
Delivery: After payment, mail arrives with a download link and a licence key.
Licence: Personal: 5 machines. Business: 25 machines. Enterprise: 100 machines. Lifetime validity.

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System

Hard disk: 150 MB of free space
RAM: 4 GB of memory minimum
Processor: 1 GHz Intel Pentium minimum and 2.4 GHz advised
Interface: English
Input: Outlook OST files

Supported editions

Windows 11 (64 bit), 10, 8 and 7 in 32-bit or 64-bit, plus Windows Server 2016, 2012 R2 and 2008.

Start OST converter with administrator rights.

Corbett has built Windows email utilities since 2020. Setup trouble and first-use questions go to our support desk.

User testimonials

OST Converter Reviews

OST converter shares 683 reviews on software index sites and customer feedback.

4.6 out of 5

Collected across 683 reviews from software indexes and customer feedback. Three reviews below are unedited.

Data moved with no loss

I need to convert my OST files to another platform so that I can free up space on my computer and access emails in Office. Corbett OST converter tool provides me with an excellent solution that does not result in data loss.

Michael Peter

Full version helped a lot

This tool can convert multiple OST files into different file formats. I purchased the full version of OST converter from Corbett's official website. It greatly aided me in completing the conversion process.

Robert Patricia

One email saved

Corbett OST converter has the ability to export the specific single email that I need to save from my OST file. This software performed admirably for a specific purpose. Special thanks to the support team for all of your assistance.

Robert Patricia

Before conversion

Prepare Your OST File for Conversion

Three short checks keep your OST conversion clean.

Find your OST file

Microsoft overview of Outlook Data Files puts OST files in drive:\Users\user\AppData\Local\Microsoft\Outlook. Show hidden folders to see them, then load that file into OST converter.

Close Outlook and copy

Quit Outlook first, then copy your OST file to a safe drive before OST converter loads it. An open Outlook can lock its own file.

Check free disk space

PDF and EML output can take more room than your OST. Select an output drive with plenty of space.

After conversion, read Import OST file to Gmail or Import OST to Thunderbird.

Best practice

How to Keep Your OST Conversion Safe

An OST conversion only helps if your mail arrives complete. Four habits keep your data safe through it.

Back up first

Copy your original OST before you start. Keep 3 copies on 2 types of media with 1 copy off site.

Start with a small OST

Convert one small OST with OST converter and open a few messages in your new format. Catch a wrong setting before a large job.

Check mail on the server

If your account is still live, confirm the server holds the same mail before you delete anything.

Keep originals until checked

Store your source OST files until folder counts match. Delete them only after you open converted mail.

Common questions

OST Converter FAQs

OST converter steps, formats, limits and licence answers.

What is an OST converter?

An OST converter opens an Outlook OST file and saves its emails and attachments in another format. Corbett OST Converter does that offline on Windows, so OST file converter needs no Outlook.

How do I convert an OST file with attachments?

Open OST converter, select Open, then Email Data Files and Outlook OST Files. Select an OST file or choose a folder, preview your mail, select Export, choose a format and press Save. Attachments stay with every message.

What is an OST file?

Microsoft overview of Outlook Data Files says Outlook stores Microsoft 365, Exchange, IMAP and Outlook.com accounts in Offline Outlook Data Files, a synced local copy of your mailbox. You cannot import from an .ost file.

Can I open an orphaned OST file?

Yes. An orphaned OST comes from a deleted profile or a closed server. OST converter loads the file by itself, so Outlook never needs to accept it.

Can I convert an OST file without Outlook?

Yes. OST converter reads your file by itself, so a PC with no Outlook installed still converts OST files. No Exchange link, internet connection or mailbox password is needed.

Which formats can I convert an OST file to?

PST, EML and MBOX for email files, plus PDF, HTML, TXT and CSV for documents. The Export menu also lists Gmail, Office 365, IMAP and Thunderbird for sending mail into an account.

How do I convert OST to PST?

Select PST in the Export menu, set options such as an individual PST for every folder and press Save. OST to PST Converter shows every click, and Import OST file into Outlook covers the Outlook side.

How do I convert OST to PDF?

Select PDF in the Export menu, search for the emails you need, choose a naming option and press Save. Every message becomes a PDF. OST to PDF Converter covers that job.

Can I convert OST to EML or MBOX?

Yes. Select EML for one file per email, or MBOX for Thunderbird and Apple Mail. Folders stay in order. Open OST to EML Converter or OST to MBOX Converter for that job.

Can I convert many OST files at once?

Yes. OST file converter loads a folder of OST files, then OST converter converts them all in one session.

Is there an OST file size limit?

No. OST converter sets no size cap, and large OST files convert too. Keep free disk space for your output.

Can I convert only some emails from an OST file?

Yes. Search by keyword with quick search, or use Advance search across every field or only name, subject, To, Cc and content, then save matched items.

Can I preview OST emails before converting?

Yes. A reading pane opens beside content, message header, properties, hex and raw message views for every email.

Does it keep my folder structure?

Yes. OST converter keeps folder hierarchy in order, so Inbox, Sent and subfolders arrive as they were.

Will converting change my original OST?

No. OST converter opens your OST read only, and output goes to a new folder. Keep a spare copy anyway.

Can I extract attachments, addresses and contacts from OST?

Yes. Save attachments alone, export addresses to CSV and pull phone numbers from message bodies. Extract attachments from OST files, Extract email addresses from OST file and Extract contacts from OST file show the steps.

Can I move OST mail into Gmail or Thunderbird?

The Export menu lists Gmail, Office 365, IMAP and Thunderbird. Read Import OST file to Gmail and Import OST to Thunderbird for the steps.

What if Outlook says my OST reached maximum size?

Convert your OST to PST, EML or MBOX with OST converter instead of forcing it open in Outlook. OST reached maximum size explains the error.

Does my OST pass through Corbett?

No. Conversion happens on your PC with no upload. Corbett never sees your OST or messages.

How many emails can free demo convert?

Free demo of OST converter opens your OST, shows every folder and gives you every search and preview. Conversion stops at 10 messages per folder, enough to test your output before you buy.

Which Windows versions work?

Windows 11 (64 bit), 10, 8 and 7, plus Windows Server 2016, 2012 R2 and 2008. There is no macOS or Linux build.

How many PCs does one licence cover?

Personal licence covers 5 machines for $99, Business covers 25 for $299 and Enterprise covers 100 for $499. All three are one time payments with lifetime validity, 24/7 support and a 30 day refund.

OST guides