MailtoPst
OST MSG

Convert OST to MSG
Online Tool

Convert OST files to MSG format online. Free tool, EU servers, GDPR compliant, auto-delete 24h. No software to install.

🛡️ GDPR Compliant 🔒 TLS 1.3 Encryption 🇪🇺 Hosted in EU 🇫🇷 Built in France 🗑️ Auto-delete 24h

What is a OST file?

OST (Offline Storage Table) is the file format used by Microsoft Outlook (Exchange cache). It stores email messages along with their metadata, attachments, and folder structure.

OST files are commonly encountered when:
- Migrating between email platforms — switching from Microsoft Outlook (Exchange cache) to another system
- Email archiving — long-term storage of email communications
- Legal and compliance — eDiscovery and regulatory requirements
- Backup and recovery — protecting email data from loss

While OST is widely used in its native ecosystem, working with these files outside of Microsoft Outlook (Exchange cache) can be challenging without proper conversion tools.

What is a MSG file?

MSG (Outlook Message) is the format used by Microsoft Outlook. It provides a structured way to store and organize email messages with full support for attachments, metadata, and folder hierarchies.

MSG is the preferred format for:
- Microsoft Outlook — native file format for import and export
- Cross-platform compatibility — supported on Windows (Outlook preferred)
- Email archiving — reliable long-term storage
- Data migration — widely accepted by email migration tools

By converting to MSG, your emails become accessible in Microsoft Outlook and compatible email applications.

Why convert OST to MSG?

Converting OST to MSG is essential in several scenarios:

1. Migrating to Microsoft Outlook
If you're moving to Microsoft Outlook, converting OST to MSG allows you to import your entire email archive with folder structure and metadata preserved.

2. Cross-platform access
OST files require Microsoft Outlook (Exchange cache) to open natively. Converting to MSG makes your emails accessible on Windows (Outlook preferred).

3. Email archiving and compliance
Organizations often need to convert email archives between formats for legal discovery, compliance requirements, or long-term storage strategies.

4. Opening emails without Microsoft Outlook (Exchange cache)
If you receive a OST file but don't have Microsoft Outlook (Exchange cache), converting to MSG lets you access the emails in Microsoft Outlook or any compatible client.

OST vs MSG — Key Differences

Feature OST MSG
Ecosystem Microsoft Exchange / Outlook Microsoft Outlook
File structure Binary database (similar to PST) OLE2 compound document
Openness Proprietary Microsoft format Proprietary Microsoft format
Platform Windows (requires Exchange profile) Windows (Outlook preferred)
Data types Email + calendar + contacts + tasks Single email with rich metadata
Free readers None without Outlook/Exchange Limited

3 methods to convert OST to MSG

Method 1: Manual conversion via email client

Import the OST file into a compatible email client, then export in MSG format. This requires having both source and target applications installed.

Pros

  • Free if you already have the software
  • Full control over the process

Cons

  • Requires specific software installed
  • Multi-step manual process
  • Time-consuming for large files
  • Risk of data loss during manual steps

Method 2: Desktop conversion software

Several desktop converters can handle the OST to MSG conversion locally. These paid tools typically cost between $29 and $99 per license.

Pros

  • Direct conversion
  • Works offline

Cons

  • Paid ($29-$99)
  • Windows only
  • Installation required
  • Limited file size support
Recommended

Method 3: MailtoPst (online, free trial)

Upload your OST file to MailtoPst, select MSG as the output, and download. Works from any browser, no software needed.

Pros

  • First conversion free
  • No Microsoft Outlook (Exchange cache) needed
  • Works on Mac, Linux, Windows
  • Preserves folder structure
  • GDPR compliant, EU servers

Cons

  • Requires internet connection
  • Paid after first conversion

Step by step

How to convert OST to MSG with MailtoPst

01

Upload your OST file

Drag & drop or click to upload your .ost file. Files up to 51 GB supported with resumable upload.

02

Choose MSG as output

Select MSG from the format dropdown. MailtoPst auto-detects the best conversion settings.

03

Download your MSG file

Conversion takes seconds. Download your .msg file or receive it by email.

Convert your OST to MSG now →

100 MB free credit. No credit card required.

FAQ

Frequently Asked Questions

Can I convert OST to MSG without Microsoft Outlook (Exchange cache)?

Yes. MailtoPst reads OST files server-side — you don't need Microsoft Outlook (Exchange cache) installed. Just upload the file from any browser on any operating system.

Will my folder structure be preserved?

Yes. MailtoPst preserves the original folder hierarchy from your OST file when converting to MSG.

Is OST to MSG conversion free?

Your first conversion is free with no credit card required. Credit packs start from €4.99.

What about attachments and metadata?

MailtoPst preserves all attachments, email headers, timestamps, read/unread status, and other metadata during the conversion.

How large can my OST file be?

MailtoPst supports files up to 50 GB with resumable upload technology. If your connection drops, you can resume where you left off.

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Ready to convert your emails?

First conversion free. No credit card required.