If you use Outlook for email, calendar, or contacts, you likely rely on PST files to store your data locally. The classic version of Outlook supports PST files with specific size limits and features. The new Outlook for Windows, currently in preview, handles PST files differently and imposes stricter limits. This article explains the key differences between PST file support in new Outlook and classic Outlook, including maximum file sizes, accessibility, and practical workarounds for users who need to manage large PST files.
Key Takeaways: PST File Limits in New vs Classic Outlook
- Classic Outlook PST size limit: Default 20 GB for Outlook 2010 and earlier; 50 GB for Outlook 2013 and later, configurable via registry.
- New Outlook PST access: Read-only in preview; no ability to create or modify PST files directly within the app.
- Workaround for large PST files: Use Outlook Data File (.pst) compression tools, archive to online archive, or split PST files with third-party utilities.
How PST Files Work in Classic Outlook and New Outlook
A PST file, or Personal Storage Table, is a data file format used by classic Outlook to store copies of messages, calendar events, contacts, and other items locally on your computer. PST files are essential for users who work offline, need to archive old emails, or want to back up their mailbox data.
In classic Outlook (Outlook 2010 through Outlook 2019, and classic Outlook for Microsoft 365), PST files are fully supported. You can create new PST files, open existing ones, export data to them, and move items between folders. The default PST file size limit is 20 GB for Outlook 2010 and earlier versions, and 50 GB for Outlook 2013 and later. This limit prevents file corruption and performance degradation. You can increase the limit by editing the Windows registry, but Microsoft does not recommend exceeding 50 GB because large PST files slow down search, sync, and backup operations.
In contrast, the new Outlook for Windows (the preview version that replaces the Mail and Calendar apps) does not fully support PST files. As of early 2025, new Outlook can only open PST files in read-only mode. You cannot create a new PST file, import items into a PST, or export data to a PST from within new Outlook. The new Outlook is designed to work primarily with cloud-based mailboxes (Exchange Online, Microsoft 365, IMAP, and POP accounts). This shift reduces the reliance on local PST files but creates challenges for users with large archives or offline storage needs.
Why Microsoft Changed PST Support in New Outlook
Microsoft is gradually moving Outlook toward a cloud-first architecture. The new Outlook uses a modern sync engine that works best with mailboxes hosted on Exchange Online or Microsoft 365. Local PST files are considered legacy storage that introduces security risks, data loss potential, and sync conflicts. By limiting PST support to read-only, Microsoft encourages users to migrate their data to cloud mailboxes or use online archives.
Steps to Manage PST Files in Classic Outlook and Work Around New Outlook Limits
If you need to work with PST files, your best option is to use classic Outlook for full read-write access. If you only have new Outlook, you must use workarounds to view or transfer PST data.
Method 1: Open a PST File in Classic Outlook (Full Access)
- Open classic Outlook
Launch the classic version of Outlook on your computer. If you have both versions installed, look for the classic Outlook icon (not the new Outlook icon). - Go to File > Open & Export > Open Outlook Data File
In the File tab, click Open & Export, then select Open Outlook Data File. A file browser window appears. - Select the PST file
Navigate to the folder containing your PST file, select it, and click Open. The PST file appears in the folder pane under your mailbox name. - Browse and copy items
You can now read, move, copy, or delete items inside the PST file. To move items to your mailbox, drag them to the desired folder.
Method 2: Open a PST File in New Outlook (Read-Only)
- Open new Outlook
Launch the new Outlook for Windows. If you do not see the new Outlook toggle in the top-right corner of classic Outlook, install it from the Microsoft Store or your Microsoft 365 admin. - Go to File > Open & Export > Open Outlook Data File
This option exists in new Outlook, but it opens the PST file in a read-only state. You cannot edit, move, or delete items. - Select the PST file
Choose your PST file and click Open. The contents appear in a separate folder. You can read emails and view calendar items, but you cannot make changes.
Method 3: Export PST Data to a Cloud Mailbox
- Open the PST in classic Outlook
If you have classic Outlook available, open the PST file using Method 1 above. - Select the folder to export
Right-click the PST folder (for example, Inbox or Archive) and choose Move > Copy to Folder. - Choose your cloud mailbox
In the Copy Items dialog, expand your email account (Exchange or Microsoft 365) and select the destination folder. Click OK. The items are copied to the cloud mailbox.
Method 4: Split a Large PST File
- Use the Outlook Import/Export tool
In classic Outlook, go to File > Open & Export > Import/Export. Choose Export to a file and click Next. - Select Outlook Data File (.pst)
Choose Outlook Data File (.pst) and click Next. Select the folder you want to export (for example, a subfolder within the large PST). - Set a smaller file size
Click Browse to choose a save location and name. Under Options, select Do not export duplicate items. Click Finish. Repeat this process for each subfolder you want to split into separate PST files.
If You Encounter PST File Errors or Limits
Classic Outlook Shows an Error That the PST File Is Too Large
When a PST file exceeds 50 GB in classic Outlook 2013 or later, Outlook may stop responding or display an error message. To work around this, reduce the PST file size by archiving older items to a new PST file or deleting unnecessary data. You can also increase the PST size limit via registry editing, but this is not recommended because performance will degrade.
New Outlook Cannot Open a PST File at All
If new Outlook fails to open a PST file, the file may be corrupted or created by an older Outlook version. First, try opening the PST in classic Outlook. If classic Outlook opens it, repair the file using the Inbox Repair Tool (Scanpst.exe). Locate Scanpst.exe in the Outlook installation folder (usually C:\Program Files\Microsoft Office\root\Office16). Run the tool, select your PST file, and click Start. After repair, try opening the PST in new Outlook again.
PST File Is Read-Only in New Outlook and Cannot Be Modified
This is by design. New Outlook does not support writing to PST files. If you need to modify items, open the PST in classic Outlook, make changes there, and then reopen it in new Outlook to see the updates. Alternatively, copy the items to your cloud mailbox and work with them there.
Classic Outlook PST vs New Outlook PST: Feature Comparison
| Item | Classic Outlook | New Outlook |
|---|---|---|
| PST file creation | Supported via File > New > Outlook Data File | Not supported |
| PST file opening | Full read-write access | Read-only access |
| Default size limit | 50 GB (Outlook 2013+), configurable | Not applicable (read-only) |
| Maximum recommended size | 50 GB for performance | Not applicable |
| Import to PST | Supported via File > Open & Export > Import/Export | Not supported |
| Export from PST | Supported via File > Open & Export > Import/Export | Not supported |
| Offline access | Full offline access to PST data | No offline access to PST data |
| Search within PST | Indexed by Windows Search | Not indexed; search may be slow |
| Backup and restore | Manual copy of PST file | Not possible directly; use cloud backup |
If you rely on PST files for archiving or offline work, classic Outlook remains the only option for full read-write access. New Outlook users should plan to migrate their data to cloud mailboxes or online archives to avoid losing functionality.