How long does the online OST to PST conversion take?

The conversion time depends on the OST file size and your internet connection speed. Smaller files can be converted within a few minutes, while larger files may take longer due to upload, processing, and download time.

Do I need to create an account or provide my email address?

Yes, creating an account is required to use the online converter. Account registration helps manage saved databases and supports security-related purposes.

Is there a limit on the number or size of OST files I can convert?

Yes, the free version allows you to convert one OST file of up to 200 MB into PST format per account. If your OST file exceeds this limit or you need additional conversions, you can upgrade to Premium (up to 5 GB).

How is my data protected, and how long are files kept?

Your file is uploaded over an encrypted TLS 1.3 connection and processed in an isolated environment. The upload is deleted after 2 hours. You can download the PST for 24 hours (Free) or 48 hours (Premium).

Will the converted PST file contain emails, contacts, calendars, tasks, and notes?

Yes, the free OST to PST converter is designed to preserve mailbox items, including emails, contacts, calendar entries, tasks, notes, and journal entries during conversion.

Will email formatting, dates, and sender details remain unchanged?

Email content, headers, sender details, timestamps, formatting and attachments are carried over. After conversion, open the PST in Outlook and check your key folders.

Can this free online OST to PST converter repair corrupted OST files?

It reads damaged OST files and recovers the items that are still readable. Success depends on how badly the file is damaged. For severe damage, try the desktop edition.

Can I convert OST files from Office 365, Exchange, or IMAP accounts?

Yes, you can convert OST files created by Office 365, Microsoft Exchange, or IMAP accounts. The converter works directly with the OST file, regardless of the account type that created it, provided the file is accessible and not severely damaged or password-locked.

How do I open the converted PST in Outlook?

In Outlook choose File, Open & Export, then Open Outlook Data File, and select the downloaded PST.

Which Outlook versions can open the PST?

The output is a Unicode PST that opens in Outlook 2013, 2016, 2019, 2021, 2024 and Microsoft 365.

Can I use the converter on Mac, Linux or a Chromebook?

Yes. The online converter works in current versions of Chrome, Edge, Firefox and Safari on Windows, macOS, Linux and Chromebook. To open the PST you need Outlook for Windows.

Should I use the online converter or the desktop edition?

Use the online converter for one file up to 200 MB (or up to 5 GB with Premium) when you do not want to install software. Use the desktop edition for very large files, batches or local PC processing. It runs on Windows.

What should I do if the online OST to PST conversion fails or gets stuck?

First, check your internet connection and ensure that the selected file is a valid OST file. Also, close Outlook if the file is currently in use. Try uploading the file again. If the OST file is very large or severely corrupted, using dedicated desktop conversion software may be necessary.

Why is the converted PST file smaller or larger than the original OST file?

OST and PST files use different storage structures. An OST file may also contain synchronization data, cached information, or space occupied by deleted items. Therefore, a difference in file size after conversion is normal and does not necessarily indicate missing mailbox data.

Which browsers are supported by the online OST to PST converter?

The online converter works with modern web browsers, including Google Chrome, Microsoft Edge, Mozilla Firefox, and Safari. For a smooth conversion experience, use an updated browser and maintain a stable internet connection, especially when uploading large OST files.

Free online tool · No Outlook needed

Free Online OST to PST Converter

MailsDaddy Online OST to PST Converter turns offline, corrupted or orphaned Outlook OST files into standard Outlook PST in your browser. It needs no Outlook or Exchange Server and is free for files up to 200 MB.

Preserves folders, attachments and email properties
Works without a running Outlook profile or Exchange server
Free up to 200 MB per file

1Upload

2Convert

3Download

Drop your .ost file hereor click to browse from your computer

Free account required · One free file up to 200 MB

Encrypted upload (TLS 1.3)·Upload deleted after 2 hours·PST available for 24h·Privacy Policy

Need local desktop batch processing?Try Desktop Version

OST → PSTin one click

Unicode PSTfor Outlook 2013 to 2024 and Microsoft 365

Free200 MB conversion quota

Windowsdesktop edition available

Quick Specifications

At a Glance Specifications

Key operational details, supported formats, system dependencies, and security limits.

Core Route

Format Pipeline

OST in → Unicode PST out

Offline Outlook cache files from Exchange Server, Microsoft 365, or IMAP accounts.

Free Tier

Quota & Limits

200 MB Free · Premium $49

Free for one file up to 200 MB per account. Premium converts files up to 5 GB for $49.

Zero Install

Dependencies

No Outlook or client needed

Runs in your browser on Windows, macOS, Linux and ChromeOS.

Universal

Compatible Files

Microsoft Outlook 2013 to 2024 & Microsoft 365 offline cache (.ost)

Supports healthy, orphaned and damaged OST files.

Strict Privacy

Security & Purge

TLS 1.3 · Auto-wiped in 2 hours

Files are deleted from servers after 2 hours. Download links expire after 24h (Free) / 48h (Premium).

Plug & Play

Outlook Compatibility

Outlook 2013–2024 & M365

Standard Unicode PST ready to import or open directly in 32-bit and 64-bit Outlook.

Common Scenarios

When to Convert OST to PST Online

Resolve inaccessible OST data, recover damaged archives, and convert without Microsoft Outlook in minutes.

Orphaned Recovery

Exchange Crashed or Tenant Dismounted

When an on-premise Exchange server fails or an Office 365 tenant is decommissioned, OST files become orphaned. Convert orphaned OST to PST online without Exchange.

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Profile Error

Outlook Profile Corruption (Error 0x8004010F)

When Outlook displays "Cannot open your default e-mail folders" or crashes upon launch, convert the OST into a Unicode PST to get your mailbox data out. Open the PST in a new or repaired Outlook profile.

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No Outlook Needed

Convert OST Without Microsoft Outlook

Need to access your OST emails on macOS, Linux, or a PC without an active MS Outlook license? Convert OST to PST directly online in your browser.

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Corruption Handling

Corrupted OST Files

OST files can become corrupted after a crash, a forced shutdown or an interrupted sync. The converter reads damaged internal blocks and recovers the items it can read into a PST.

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Cloud Engine • No Local Dependencies

Why Convert OST to PST Without Outlook?

Converting an Outlook OST file typically requires an active Outlook profile and the original email account. When an Outlook profile is damaged, an account is decommissioned, or you are working on a computer without Microsoft Office, standard export tools cannot help. MailsDaddy Free Online OST to PST Converter processes your OST file directly in the browser so you can convert orphaned or inaccessible OST files into standard Unicode PST format without installing Microsoft Outlook.

No Microsoft Outlook Installation Needed

Convert OST files directly from Chrome, Edge, Firefox, or Safari on Windows, macOS, Linux, or ChromeOS.

No Exchange Server Connection

Standard Outlook requires an active Exchange connection to open cached OST files. Our online tool extracts mailbox data independently.

Bypass Outlook Profile Errors

Access your mailbox data when Outlook fails to open with error 0x8004010F or damaged MAPI profiles.

Damaged File Recovery

How We Handle Corrupted & Damaged OST Files

OST files can be damaged by sudden shutdowns, aborted synchronisations or by growing very large. The converter reads the damaged file and recovers the items that are still readable. Very badly damaged files can still lose some items; the desktop edition scans more deeply.

Deep Block-Level Parsing

Scans the raw binary structures of damaged OST files, bypassing broken header pointers to recover intact message objects, MIME bodies, and attachments.

Orphaned Item Reconstruction

Recovers orphaned mail items where they can be read and places them in recovered folders.

Unicode PST Generation

Creates a Unicode PST that opens in Outlook 2024, 2021, 2019, 2016, 2013 and Microsoft 365.

3 Simple Steps

How to convert OST to PST online

The whole conversion process is designed so you can complete it in minutes without installing software.

Upload your OST file

Select your .ost file or drag it into the upload box. Files up to 200 MB are free.

Convert to PST

The cloud converter reads the OST messages, attachments and folders and builds a clean Unicode PST.

Download the PST

Download the PST from the result screen. It stays available for 24 hours on the free plan and 48 hours with Premium.

Outlook Import Guide

How to Import Converted OST PST into Microsoft Outlook

Compatible with Microsoft Outlook 365, 2024, 2021, 2019, 2016, and 2013 on Windows.

Open Outlook on Windows

Start Microsoft Outlook (Microsoft 365, 2024, 2021, 2019, 2016, or 2013) on your computer.

Select Open Outlook Data File

In the top menu bar, click File > Open & Export > Open Outlook Data File (.pst).

Access Restored OST Folders

Browse and select the downloaded PST file. Your folders, emails, headers, and attachments will appear in the navigation pane.

What is converted

Your folders, emails, attachments, contacts, calendars, tasks and notes are carried over into an Outlook PST.

Folder structure preserved

All folders and subfolders are mirrored in the output PST with clean directory trees.

Emails & message attributes

Retains full HTML/RTF styling, inline images, To, From, CC, BCC, Subject headers, and message flags.

Attachments & documents

Attachments and inline images stay with their original messages, including PDFs, Office docs, spreadsheets, and ZIP files.

Contacts & address books

Contact profiles, display names, email addresses, phone numbers, and notes are preserved in the PST.

Calendars & meeting schedules

Preserves appointments, recurring schedules, attendee invitations, locations, and reminder notifications.

Tasks, reminders & notes

Migrates to-do tasks, priorities, due dates, reminder alarms, and sticky memo notes into your new Outlook PST.

Available Online Tools:Free Online OST to PST Free Online MBOX to PST Free Online OLM to PSTOutput: Unicode PST (Outlook 2013 to 2024 & Microsoft 365)

Free vs Full

Start free. Upgrade when you need everything.

The free tier is enough to confirm your mailbox opens correctly before you commit.

Online ServiceStarter

Free

$0/ 1 Free File

Convert OST File

Instant Access · Free Quota Included

File size up to 200 MB
Convert single file for Free
Free account required, one file per account
Free Conversion available for 24 hours to download

Best Value

Online ServiceHigh Capacity

Premium

$29/ Single File

Secure Online Transaction via PayPro Global

File Size limit is upto 5 GB
Convert Single File at $29
Converted file available for 48 hours to download

Desktop SoftwareDesktop App

Personal Edition

$49/ Lifetime License

Try Desktop Software

Local desktop processing • No size limit. Batch conversion and local PC processing ($49). Licence for up to 2 PCs

No file size limit
Batch conversion of unlimited files at $49
Licence for up to 2 PCs • Offline PC processing
Converted File on system for unlimited period

TLS 1.3 encrypted uploadAuto-purge Data PrivacyFolder Structure Preserved

MailsDaddy® Cloud Conversion Engine

Comparison Matrix

Online OST Converter vs Desktop Edition

Compare the free online web app against desktop software and manual export.

Cost & Access

Free ($0) up to 200 MB

Upgrade available for large files up to 5 GB

Software Needed

Zero Installation

Runs in your browser (no Outlook)

Max Mailbox Size

200 MB (Free) / 5 GB (Premium)

Fast cloud conversion pipeline

Batch Processing

Single File Pipeline

Converts 1 file at a time

Damaged Archives

Automated Cloud Repair

Recovers readable items & headers

Operating System

Any OS (Browser-Based)

Windows, macOS, Linux, ChromeOS

Privacy & Retention

TLS 1.3 · Auto-Wiped in 2h

PST link active 24h (Free) / 48h (Paid)

Convert Online Free Explore Desktop Edition ($49)

Feature	Online OST ConverterCurrent	Desktop Edition	Manual Method
Cost & Access	Free ($0) up to 200 MB Upgrade available for large files up to 5 GB	Lifetime License ($49) Licence for up to 2 PCs, unlimited usage	Free, needs Outlook or source client Needs a mail account or server
Software Needed	Zero Installation Runs in your browser (no Outlook)	Windows Desktop App Offline processing on your PC	Multiple Desktop Apps Requires Outlook + source client
Max Mailbox Size	200 MB (Free) / 5 GB (Premium) Fast cloud conversion pipeline	No File Size Limit Tested on large archives	Depends on your email client May fail on large mailboxes
Batch Processing	Single File Pipeline Converts 1 file at a time	Simultaneous Batch Mode Batch conversion of multiple files	Manual Export / Sync Drag & drop folder by folder
Damaged Archives	Automated Cloud Repair Recovers readable items & headers	Advanced Deep Scan Offline processing on your PC	May fail on damaged files Clients abort on broken records
Operating System	Any OS (Browser-Based) Windows, macOS, Linux, ChromeOS	Windows Only Windows 11, 10, 8, 7 & Server	OS Restricted Limited to client OS support
Privacy & Retention	TLS 1.3 · Auto-Wiped in 2h PST link active 24h (Free) / 48h (Paid)	Completely Offline Processing Data never leaves your computer	Syncs to Mail Server Best for small, healthy mailboxes
Recommendation:	Convert Online Free	Get Desktop ($49)	High risk of corruption & Outlook crashes

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Convert Mac Outlook OLM archives into Windows Outlook PST online without Outlook or Mac hardware.

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FAQ

Frequently Asked Questions

Clear, detailed answers about OST conversion, Outlook compatibility, and data privacy.

An OST (Offline Storage Table) file is the local copy of a mailbox that Outlook keeps when it is connected to Exchange, Microsoft 365 or IMAP. It lets you work offline and syncs when you reconnect.

Get your mailbox back today.

Upload your OST file and download an Outlook PST in a few clicks.

Start converting