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OST MBOX

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

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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 MBOX file?

MBOX (Mailbox) is the format used by Thunderbird, Gmail, Unix mail. It provides a structured way to store and organize email messages with full support for attachments, metadata, and folder hierarchies.

MBOX is the preferred format for:
- Thunderbird, Gmail, Unix mail — native file format for import and export
- Cross-platform compatibility — supported on Any OS (cross-platform)
- Email archiving — reliable long-term storage
- Data migration — widely accepted by email migration tools

By converting to MBOX, your emails become accessible in Thunderbird, Gmail, Unix mail and compatible email applications.

Why convert OST to MBOX?

Converting OST to MBOX is essential in several scenarios:

1. Migrating to Thunderbird, Gmail, Unix mail
If you're moving to Thunderbird, Gmail, Unix mail, converting OST to MBOX 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 MBOX makes your emails accessible on Any OS (cross-platform).

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 MBOX lets you access the emails in Thunderbird, Gmail, Unix mail or any compatible client.

OST vs MBOX — Key Differences

Feature OST MBOX
Ecosystem Microsoft Exchange / Outlook Universal (Thunderbird, Gmail, Apple Mail...)
File structure Binary database (similar to PST) Plain text, emails concatenated
Openness Proprietary Microsoft format Open standard (RFC 4155)
Platform Windows (requires Exchange profile) Any OS (cross-platform)
Data types Email + calendar + contacts + tasks Email only
Free readers None without Outlook/Exchange Many free clients available

3 methods to convert OST to MBOX

Method 1: Manual conversion via email client

Import the OST file into a compatible email client, then export in MBOX 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 MBOX 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 MBOX 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
Try MailtoPst →

Step by step

How to convert OST to MBOX 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 MBOX as output

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

03

Download your MBOX file

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

Convert your OST to MBOX now →

100 MB free credit. No credit card required.

FAQ

Frequently Asked Questions

Can I convert OST to MBOX 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 MBOX.

Is OST to MBOX 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.

Related conversions

MBOX → MSG MBOX → EML MBOX → PST OST → PST PST → MBOX
See all 30 conversion paths →

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