Classic Outlook PST Files in New Outlook: What Still Needs Classic Outlook

Many users have PST files from older versions of Outlook and want to use them in the new Outlook for Windows. The new Outlook does not directly open or manage PST files the way classic Outlook does. This article explains what PST files are, why the new Outlook handles them differently, and which tasks still require classic Outlook.

PST files store your emails, calendar items, contacts, and tasks locally on your computer. Classic Outlook can open multiple PST files side by side, archive data into PST files, and export to PST format. The new Outlook uses a different data model that relies on Microsoft 365 cloud storage or Exchange Online. As a result, several PST-related features are missing or work differently in the new app.

This article covers the exact limitations of the new Outlook regarding PST files, the tasks that still need classic Outlook, and what you can do to work around these restrictions.

What PST Files Are and How Classic Outlook Uses Them

A PST file, short for Personal Storage Table, is a database file that contains your Outlook data. It stores emails, calendar events, contacts, tasks, notes, and journal entries on your local hard drive. Classic Outlook creates a PST file automatically when you set up a POP3 or IMAP account. It also uses PST files for archiving old items through the AutoArchive feature.

In classic Outlook, you can open multiple PST files simultaneously by going to File > Open & Export > Open Outlook Data File. Each PST file appears as a separate folder set in the navigation pane. You can copy or move items between PST files, search across all open PST files, and close PST files when you no longer need them.

Classic Outlook also allows exporting any folder to a PST file. You can create a new PST file, name it, set a password, and choose a compression format. This is useful for backing up data, transferring data to another computer, or reducing the size of your main mailbox.

How the New Outlook Stores Data

The new Outlook for Windows does not use PST files for local storage. Instead, it synchronizes data directly with Microsoft 365 mailboxes, Exchange Online, or supported third-party accounts like Gmail and Yahoo. The new app relies on cloud storage and does not maintain a local data file that users can access or manipulate.

When you add an account to the new Outlook, the app downloads a cached copy of your mailbox data. This cache is stored in a proprietary format that is not accessible through File Explorer or any Outlook data file management tool. You cannot open this cache as a PST file, nor can you attach it to another Outlook profile.

Steps to Identify Which PST Tasks Still Need Classic Outlook

Follow these steps to check which PST-related operations require classic Outlook. If you do not have classic Outlook installed, you can download it from the Microsoft 365 portal or use the version that came with Office 2021 or earlier.

1. Check if you have classic Outlook installed
   Open the Start menu and type “Outlook”. If you see two Outlook entries, one named “Outlook” and one named “Outlook (classic)”, the classic version is available. If you see only one Outlook entry, right-click it and select Open file location. If the file name is OUTLOOK.EXE and the path includes “root\Office16”, it is classic Outlook. If the path includes “WindowsApps”, it is the new Outlook.
2. Open an existing PST file in the new Outlook
   In the new Outlook, go to File > Open & Export. You will see options to open a calendar, an email file (MSG format), or an Outlook data file. Click “Open Outlook Data File”. If the new Outlook does not respond or shows an error message, it cannot open PST files. This confirms you need classic Outlook.
3. Try to import a PST file into the new Outlook
   Go to File > Open & Export > Import/Export. The new Outlook may show only one option: “Import from another program or file”. Click Next and select “Outlook Data File (.pst)”. If the next screen asks for a file path and then fails with “This operation is not supported”, the import function is blocked. Classic Outlook is required for PST import.
4. Attempt to export data to a PST file
   In the new Outlook, go to File > Open & Export > Import/Export. Select “Export to a file” and click Next. Choose “Outlook Data File (.pst)”. If the export wizard does not proceed or displays “This feature is not available in the new Outlook”, you must use classic Outlook to export to PST.
5. Test AutoArchive settings
   In the new Outlook, go to File > Options > Mail. Look for the “AutoArchive” section. If the option “AutoArchive settings” is missing entirely, the new Outlook does not support AutoArchive. Classic Outlook has this feature under File > Options > Advanced > AutoArchive Settings.

If You Still Need Classic Outlook: Related Limitations

Even if you have classic Outlook installed, you may encounter issues when trying to work with PST files alongside the new Outlook. Below are the most common problems and how to solve them.

New Outlook Replaces Classic Outlook as the Default Mail App

After installing the new Outlook, Windows may set it as the default email application. Double-clicking a PST file in File Explorer will attempt to open it in the new Outlook and fail. To fix this, go to Settings > Apps > Default apps. Scroll to “Email” and change the default from “Outlook (new)” to “Outlook (classic)”. After this, PST files will open in classic Outlook.

Classic Outlook Cannot Open a PST File That Was Created by the New Outlook

The new Outlook does not create PST files, but it can export data to a PST file if you use a third-party tool. If you export data from the new Outlook using a migration tool and then try to open that PST file in classic Outlook, you may see a compatibility error. Use classic Outlook’s ScanPST.exe tool to repair the file. ScanPST.exe is located in the Office installation folder, typically C:\Program Files\Microsoft Office\root\Office16.

Multiple PST Files Cause Performance Issues in Classic Outlook

If you keep many PST files open in classic Outlook, the application may become slow or crash. Classic Outlook loads each PST file into memory. To improve performance, close PST files you do not need by right-clicking the PST folder in the navigation pane and selecting “Close ““”. Alternatively, merge smaller PST files into one using the Import/Export wizard.

Item	Classic Outlook	New Outlook
Open PST files	Yes, multiple PST files supported	Not supported
Import from PST	Yes, via File > Open & Export > Import/Export	Not supported
Export to PST	Yes, creates standard PST files	Not supported
AutoArchive to PST	Yes, configurable per folder	Not available
Manage PST in Account Settings	Yes, Data Files tab shows all PST files	No Data Files tab
Password-protected PST	Yes, supports encryption	Cannot open password-protected PST
Search across PST files	Yes, instant search works	Cannot search PST content

The new Outlook is designed for cloud-first workflows. If you rely on PST files for local archiving, data portability, or offline access to old data, you must keep classic Outlook installed. Microsoft has not announced plans to add PST support to the new Outlook. As of 2025, classic Outlook remains the only option for working with PST files.

You can run both versions side by side on the same computer. Use the new Outlook for your daily Microsoft 365 email and calendar tasks. Use classic Outlook only when you need to open, import, export, or archive PST files. To switch between versions, go to the new Outlook’s title bar, click the toggle button labeled “Try the new Outlook” or “Try the classic Outlook”, and confirm the switch.

For users who manage large PST archives, consider migrating old PST data to a Microsoft 365 archive mailbox or a shared mailbox. This allows you to access all historical data from the new Outlook without needing classic Outlook. To migrate, use classic Outlook’s Export to PST feature, then use the Microsoft 365 Migration tool or a third-party service to upload the PST to Exchange Online.