How to Convert OST to PST Free – Tech Guide for Early 2027

Written By Afiya Jafar Afiya Jafar Technology & Digital Trends Writer Afiya Jafar is a technology writer with 5+ years of experience covering technology, digital trends, artificial intelligence, software, gadgets, cybersecurity and emerging technologies. View Author Profile →

Reviewed By Sameena Begum Sameena Begum Technology & Digital Content Reviewer Sameena Begum is a **technology and digital content reviewer** who reviews selected articles to help ensure that information is presented clearly, accurately, and responsibly. View Reviewer Profile →

Published on October 28, 2026

Last Updated on October 28, 2026

Quick answer: To convert OST to PST for free, open classic Outlook and go to File > Open & Export > Import/Export > Export to a file > Outlook Data File (.pst), then select your mailbox and save. This works only while your email account still connects. For an orphaned or corrupted OST, you need an OST to PST converter.

That answer has not changed in years. What has changed is the reason so many people are searching for it right now. Microsoft is moving Windows users from classic Outlook to the new Outlook, and the new app does not keep your mail in an OST file the way classic Outlook does. If you have years of email sitting in an OST, early 2027 is a good time to turn it into a PST you control.

This guide helps you pick the right method for your situation in under a minute, then walks you through each one.

Why OST to PST Matters More in 2027

In March 2027, the new Outlook becomes the default for business users on Windows. Microsoft moved this “opt-out” phase from April 2026 to March 2027 to give organizations 12 months to prepare (Microsoft 365 Message Center MC949965). Users can still switch back to classic Outlook for now. The final cutover, when classic Outlook is removed, will come no earlier than March 2028, and classic Outlook could stay available until 2029 (Directions on Microsoft).

What this means for your OST file: your OST is only readable by the classic Outlook profile that created it. The new Outlook stores offline mail differently and does not open that OST. When you switch, your server mailbox simply syncs again, but anything that lived only in the local file can be left behind.

That is why early 2027 is the right moment to act. Exporting to PST now gives you:

• A portable backup you can open in classic Outlook, or import into the new Outlook.
• A copy of local-only folders and old archives that will not sync to the new app.
• Peace of mind before your IT team or Windows update flips the switch.

OST vs PST in one line: an OST is a locked, synced copy of your mailbox tied to one PC; a PST is a standalone file you can move, back up and open anywhere.

Top 4 Free Methods to Convert OST File to PST

Method 1: Using Outlook Import/Export Wizard

The Import/Export Wizard is the most complete free way to convert OST to PST. It copies your emails, contacts, calendar, tasks and notes into one PST file, with the folder structure intact.

Use it when: your account still opens in classic Outlook and you want a full backup, especially before moving to the new Outlook or a new PC.

Steps:

1. Open classic Outlook and click File > Open & Export > Import/Export.
2. Select Export to a file and click Next.
3. Choose Outlook Data File (.pst) and click Next.
4. Click your account name at the top of the folder list so the whole mailbox is selected, and tick Include subfolders.
5. Optional: click Filter to export only a date range, such as everything before 2025.
6. Click Browse, choose a safe location, and select Do not export duplicate items.
7. Click Finish. You can add a password, or click OK to skip it.

Method 2: Using Outlook Archive Feature

Outlook’s Archive feature moves older items out of your mailbox and into a PST file. It is the best free option when your mailbox is close to its size limit and you want to keep old mail without deleting it.

Use it when: you want old emails (say, older than two years) stored in a PST, and your current mailbox kept lean.

Steps:

1. In classic Outlook, click File > Tools > Clean Up Old Items. (In some versions this button is called Archive.)
2. Select Archive this folder and all subfolders, then click the folder or the whole mailbox.
3. Set a date in Archive items older than.
4. Tick Include items with “Do not AutoArchive” checked if you want everything captured.
5. Click Browse to name the PST and choose where to save it, then click OK.

Method 3: Using Drag & Drop Method

Drag and drop is the fastest free method when you only need part of your mailbox, such as one client’s folder or a single project’s emails.

Use it when: you want to save a few selected folders, not the whole mailbox.

Steps:

1. In classic Outlook, click Home > New Items > More Items > Outlook Data File.
2. Name the new PST, choose a location, and click OK. It appears at the bottom of your folder pane.
3. Right-click the new PST and create folders to match the ones you want to copy.
4. Select the emails (press Ctrl + A for a whole folder), hold Ctrl, and drag them into the PST folder. Holding Ctrl copies the items rather than moving them.
5. When finished, right-click the PST and choose Close so the file is safe to move.

Method 4: Using a Professional Online OST to PST Converter

When Methods 1 to 3 fail because the account is gone or the OST is damaged, an online converter is the fastest fix. Our pick is Stellar Online OST Converter, a browser-based tool from Stellar, a data recovery company working since 1993. It converts OST to PST without Outlook, without an Exchange connection and without installing anything.

Why we recommend Stellar Online OST Converter:

• Free for small files: OST files under 500 MB convert at no cost, with no credit card needed.
• No Outlook or Exchange needed: everything runs in your browser, on Chrome, Edge, Firefox or Safari.
• Complete mailbox conversion: emails, attachments, contacts, calendars, tasks, notes and journals are kept, along with the original folder structure.
• Preview before download: for files up to 500 MB, you can check the folder structure and item count in your browser first.
• Wide compatibility: supports OST files from Outlook 2003 to 2021, in both ANSI and Unicode formats, including password-protected OST files.
• Privacy built in: uploads use SSL encryption, conversion is fully automated, and files are permanently deleted from Stellar’s servers after 24 hours (Free) or 48 hours (Premium).

How to convert OST to PST with Stellar Online OST Converter:

1. Open Stellar Online OST Converter and sign in.
2. Click Convert OST File and upload your OST.
3. Track the upload and conversion progress on screen. Stellar says most files are ready within 15 minutes.
4. Preview the converted folders and item count to confirm your data is complete.
5. Download the PST file, then open it in Outlook with File > Open & Export > Open Outlook Data File.

Plans and pricing:

Prices as listed on Stellar’s website in October 2026.

Good to Know: Stellar also offers a desktop-based OST to PST converter for users who need to process larger OST files or prefer a dedicated application. Unlike the online tool, desktop software can be a suitable alternative when your file exceeds the online converter’s size limits or you need additional conversion options. Choose the solution that best fits your file size, conversion requirements, and preferences.

Conclusion:

If your account still opens in classic Outlook, convert your OST to PST for free with the Import/Export Wizard, and do it before the new Outlook becomes your default in 2027. Use Archive to slim down a full mailbox and Drag & Drop for a few folders. Keep an online converter in reserve for orphaned or corrupted OST files, and always preview before you pay.

Frequently Asked Questions

How do I convert OST to PST without Outlook?

You need an OST to PST converter (Method 4). Outlook’s built-in tools only work inside the Outlook profile that created the OST, so without Outlook there is no free manual option.

Can I convert an orphaned OST file to PST for free?

Only partly. Manual methods cannot open an orphaned OST. Many converters offer a free preview or convert a small number of items, which can be enough for a few important emails.

Does the new Outlook use OST files?

No. The new Outlook stores offline data differently and cannot open the OST file created by classic Outlook. Export your OST data to PST before you switch.

Is there a size limit for PST files?

Outlook 2010 and later create PST files with a default limit of 50 GB. For large mailboxes, export to several smaller PST files, for example by year.

How long does OST to PST conversion take?

It depends on mailbox size and your PC. Small mailboxes take a few minutes; mailboxes over 10 GB can take an hour or more, so run large exports when you do not need Outlook.

About the Author & Reviewer

AUTHOR

WRITTEN BY

Afiya Jafar

Technology & Digital Trends Writer

Afiya Jafar is a technology writer with 5+ years of experience covering artificial intelligence, software, applications, gadgets, cybersecurity, cloud computing, internet technologies and emerging technology trends.

AUTHOR PROFILE →

REVIEWER

REVIEWED BY

Sameena Begum

Technology & Digital Content Reviewer

Sameena Begum is a **technology and digital content reviewer** who reviews selected articles to help ensure that information is presented clearly, accurately, and responsibly.

REVIEWER PROFILE →