New Outlook can't open your PST file?

New Outlook for Windows can open a PST file only when classic Outlook is also installed, your account has a Microsoft 365 subscription, and the PC is not an ARM device. If any of those is missing, a standalone reader such as Mailbox Rescue opens the file instead.

What does Microsoft require?

According to Microsoft's support article on PST files in new Outlook, opening a PST in new Outlook needs:

classic Outlook installed on the same PC, with the same 32/64-bit version;
a Microsoft 365 subscription;
a PC that is not ARM-based (Snapdragon laptops are left out).

That leaves out people without Microsoft 365, ARM laptops, and anyone who removed classic Outlook.

How to open the PST anyway

Download Mailbox Rescue (there is a native ARM version).
Open the PST, read and search everything.
Export to EML or MBOX to keep the mail in a format that doesn't depend on Outlook.

Download free for Windows Full version: $9.99 once

Windows 10 and 11, Intel/AMD and ARM. No account needed. Works offline.

Frequently asked questions

Do I need Outlook or a Microsoft 365 subscription?

No. Mailbox Rescue reads PST, OST and MSG files directly. Outlook does not need to be installed, and no Microsoft account or subscription is needed.

Is my mailbox uploaded anywhere?

No. Everything happens on your PC. The only thing the app ever sends over the internet is your licence key when you unlock the full version.

What does the free version do?

It opens, searches and shows every message, and saves single attachments, without limits. Bulk export stops after 25 messages so you can check the result before you buy.

Is it a subscription?

No. The full version is $9.99 once and works on up to 3 PCs.

Updated 2026-11-08