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Convert OST to PST
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Convert Outlook OST files to PST format. Recover emails from orphaned, corrupted, or inaccessible OST files. EU servers, GDPR compliant.

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What is a OST file?

OST (Offline Storage Table) is Microsoft Outlook's format for storing a local, synchronized copy of your Exchange or Microsoft 365 mailbox. When you use Outlook with an Exchange server, all your emails are cached locally in an .ost file so you can work offline.

Key characteristics of OST:
- Tied to a specific profile — an OST file is linked to the Outlook profile and Exchange account that created it
- Automatic sync — Outlook keeps the OST in sync with the server when online
- Cannot be opened independently — unlike PST, you can't simply open an OST file in Outlook
- Common location — typically found in `%LOCALAPPDATA%\Microsoft\Outlook\`

OST files become problematic when:
- The Exchange server is decommissioned
- A user account is deleted or disabled
- The Outlook profile is corrupted
- An employee leaves and their mailbox is archived

In these scenarios, the OST file becomes 'orphaned' — it still contains all the emails, but Outlook can't open it because the server profile no longer exists.

What is a PST file?

PST (Personal Storage Table) is Microsoft Outlook's portable format for storing email data independently of any server or profile. Unlike OST, a PST file can be opened by anyone with Outlook — making it the universal format for email archiving and sharing.

Key advantages of PST over OST:
- Portable — can be opened on any computer with Outlook
- No server dependency — works completely offline
- Shareable — can be copied and sent to colleagues or legal teams
- Importable — can be imported into any Outlook installation
- Archival standard — the industry standard for email preservation

Why convert OST to PST?

OST to PST conversion is critical in several enterprise scenarios:

1. Recovering orphaned OST files
When an Exchange account is deleted or a server is decommissioned, the local OST file becomes orphaned. Converting to PST recovers all emails, contacts, and calendar items from the otherwise inaccessible file.

2. Employee offboarding
When an employee leaves, their Exchange mailbox may be deactivated, but the local OST file on their computer still contains all their emails. Converting to PST preserves this data for compliance.

3. Corrupted Outlook profile
If an Outlook profile becomes corrupted, the associated OST file can't be opened through normal means. Converting to PST bypasses the corrupted profile and recovers the data.

4. Email archiving and backup
PST files are the standard for long-term email archiving. Converting OST to PST creates a portable, independent backup that doesn't depend on any server infrastructure.

OST vs PST — Key Differences

Feature OST PST
File purpose Local cache of Exchange mailbox Independent portable archive
Server dependency Requires linked Exchange/365 account No server needed, fully portable
Portability Locked to creating profile/machine Can be opened on any Outlook install
Created by Outlook automatically (Exchange/IMAP) User-created or exported
Max file size 50 GB (same as PST) 50 GB (Outlook 2010+)
Recovery when orphaned Requires conversion tool Always accessible
Sharing Cannot be shared or transferred Easy to share and transfer
Backup Not suitable for backup Standard backup format

3 methods to convert OST to PST

Method 1: Archive from Outlook (if profile works)

If your Outlook profile is still connected to the Exchange server, you can use File > Import/Export > Export to a PST to create a PST file from the cached data.

Pros

  • ✓ Free, built into Outlook
  • ✓ Official Microsoft method

Cons

  • ✗ Only works if profile is intact and server is accessible
  • ✗ Useless for orphaned OST files
  • ✗ Slow for large mailboxes

Method 2: Desktop recovery software

Several desktop recovery tools can read orphaned OST files and convert them to PST locally. These paid applications typically cost between $49 and $199 per license.

Pros

  • ✓ Works with orphaned OST files
  • ✓ Handles corrupted files

Cons

  • ✗ Expensive ($49-$199)
  • ✗ Windows only
  • ✗ Slow local processing
  • ✗ Some tools have output size limits in free version
Recommended

Method 3: MailtoPst (online, free trial)

Upload your orphaned or inaccessible OST file to MailtoPst. Our cloud engine reads the OST structure directly and converts it to a clean PST file. No Outlook or Exchange needed.

Pros

  • ✓ Works with orphaned OST files
  • ✓ First conversion free
  • ✓ No Outlook or Exchange needed
  • ✓ Handles corrupted OST files
  • ✓ EU servers, GDPR compliant
  • ✓ Files up to 51 GB

Cons

  • ✗ Requires internet connection
  • ✗ Paid credits after first conversion
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Step by step

How to convert OST to PST 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 PST as output

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

03

Download your PST file

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

Convert your OST to PST now →

First conversion free. No credit card required.

FAQ

Frequently Asked Questions

Can I convert an orphaned OST file to PST?

Yes. MailtoPst reads OST files directly without needing the original Exchange server or Outlook profile. This makes it ideal for recovering orphaned OST files.

Can MailtoPst recover a corrupted OST file?

MailtoPst can recover data from many corrupted OST files. Our engine attempts to read and extract all readable email items, even if some parts of the file are damaged.

Where is my OST file located?

On Windows, OST files are typically found in: C:\Users\[YourName]\AppData\Local\Microsoft\Outlook\. You can also find the exact path in Outlook: File > Account Settings > Data Files.

Will calendar events and contacts be preserved?

Yes. The OST to PST conversion preserves all item types: emails, calendar events, contacts, tasks, notes, and journal entries, along with all their metadata.

Is the OST to PST conversion free?

Your first conversion is free with no credit card required. Credit packs start from €4.99 for 5 conversions.

What's the difference between OST and PST?

OST is a local cache of an Exchange/365 mailbox, tied to a specific profile and server. PST is a portable archive that can be opened independently. When the server is gone, OST becomes useless — PST remains accessible forever.

Related conversions

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

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