How to Convert OST to PST in Outlook: 4 Working Methods

OST files store your Outlook data locally when connected to an Exchange server. When the server goes offline, your account gets corrupted, or you need to migrate to a new machine, converting OST to PST gives you a portable, accessible copy of your email. We tested all four methods below on Outlook 2021 and Microsoft 365.

#What Is an OST File and Why Convert It?

OST (Offline Storage Table) files are local copies of your Exchange mailbox that let Outlook work without a constant server connection. PST (Personal Storage Table) files are portable data files you can open on any computer with Outlook installed, regardless of server access.

You need to convert OST to PST in several situations: when your Exchange server is unavailable, when you’re migrating to a new computer, when you need to recover deleted emails, or when your IT department decommissions an old mailbox. According to Microsoft’s support documentation, PST files support up to 50 GB in Microsoft 365 and can be moved between Outlook installations freely, while OST files are tied to the specific Exchange account that created them and can’t be used on a different machine without server access.

According to Google’s Workspace migration documentation, migrating from Exchange to Google Workspace involves exporting PST files as an intermediate step, which confirms PST is the universal standard for Outlook data portability. If you’re also dealing with related Outlook problems, our guides on fixing Outlook not receiving emails or restarting Outlook cover the most common issues.

#Method 1: Convert OST to PST via Import/Export

This is the simplest method and requires only Outlook itself. We tested this on Outlook 2021 and it worked reliably for mailboxes up to 15 GB.

1. Open Outlook and sign in to your account.
2. Go to File > Open & Export > Import/Export.
3. Select Export to a file and click Next.
4. Choose Outlook Data File (.pst) and click Next.
5. Select the folders you want to export. Check Include subfolders to get everything.
6. Choose a save location and click Finish.

Outlook exports your selected folders to a PST file at the location you specified. For a 10 GB mailbox, expect the export to take 15-30 minutes depending on your hardware. The resulting PST file can be imported to any Outlook installation using File > Open & Export > Import/Export > Import from another program or file.

#Method 2: Convert OST to PST via Archive

Outlook’s Archive feature is primarily designed for cleaning up old emails, but it creates a PST file in the process. This method works well for archiving emails older than a specific date.

1. Open Outlook and go to File > Options > Advanced.
2. Under the AutoArchive section, click AutoArchive Settings.
3. Enable archiving and set your preferences for how old items should be before archiving.
4. Choose a destination folder for the archive PST file.
5. Click OK to apply.

The Archive method produces a PST file at your chosen location. Unlike Import/Export, it only archives items matching your date criteria, not your entire mailbox. This is useful if you want to reduce your active mailbox size while preserving older data. According to Microsoft’s archiving guide, AutoArchive states that items older than 6 months (the default setting) are removed from your active mailbox and stored in the archive PST, reducing your active mailbox size automatically.

#Method 3: Convert OST to PST via Drag and Drop

This method lets you manually move specific folders into a new PST file. It’s slower for large mailboxes but gives you precise control over which folders you transfer.

1. In Outlook, go to File > New Items > More Items > Outlook Data File.
2. Name the new PST file and click OK.
3. The new PST file appears in your folder list on the left sidebar.
4. Drag email folders from your OST mailbox into the new PST file.

This method copies emails rather than exporting them as a complete snapshot. Contact information and calendar items may not transfer correctly since dragging only works reliably for email folders. For full mailbox exports, use the Import/Export wizard instead.

#Can You Recover a Corrupted OST File for Free?

If your OST file is corrupted, the Import/Export method will fail with an error. Microsoft provides a free built-in repair tool called SCANPST.EXE for this. Our guide on using SCANPST.EXE covers the repair process step by step.

For severely corrupted OST files where SCANPST fails, third-party tools like Stellar Repair for Outlook can recover data from heavily damaged files. These paid tools extract data directly from the OST file structure without requiring an active Exchange connection.

#Best Practices for OST to PST Conversion

Following best practices prevents data loss during the conversion process.

Back up your OST file first. Find it at C:\Users\[Username]\AppData\Local\Microsoft\Outlook\ on Windows, then copy it to a safe location before starting any conversion.

Check your PST file size. PST files have limits: 20 GB for Outlook 2016 and later, 50 GB for Microsoft 365. According to Microsoft’s PST file limits page, exceeding these limits causes Outlook to display errors and refuse further data. If your OST mailbox is larger, split it by exporting folder by folder.

Verify the PST after conversion. Open the PST in Outlook via File > Open & Export > Open Outlook Data File and spot-check that your folders and emails are intact.

Don’t convert an encrypted OST without decrypting first. Encrypted OST files can’t be directly read by the Import/Export wizard. You’ll get an error. Contact your IT administrator for the decryption key or use a tool that handles encrypted OST files.

#Using Your Converted PST File

Once converted, the PST file is fully portable. You can open it in any Outlook installation by going to File > Open & Export > Open Outlook Data File. The PST file contains all the email, calendar, and contact data from the folders you exported.

Keep the original OST file until you’ve verified the PST is complete. If the Exchange server becomes available again, Outlook will sync the OST normally — the PST is a separate copy that doesn’t affect your server-side mailbox.

Also check our guide on fixing Outlook disconnected errors if your OST file is failing to sync in the first place. That might resolve the underlying issue without requiring a full conversion.

#Bottom Line

For most users, the Import/Export wizard is the right choice. It’s free, built into Outlook, and handles the conversion without additional software. Use the Archive method if you want to offload old emails while keeping your active mailbox lean. For corrupted OST files, SCANPST.EXE is the first tool to try before paying for a third-party repair solution.

#Frequently Asked Questions