The short answer
- PST is an Outlook data file format that stores and transfers email, contacts and calendar information, but a PST export does not preserve every account setting.
- In classic Outlook, choose File → Open & Export → Open Outlook Data File, select the PST, then expand its folders and search for messages. New Outlook can open, read and search PST email, but requires a Microsoft 365 subscription and classic Outlook installed with matching bitness. New Outlook for ARM does not support PST.
- Assess attachments separately when handling an untrusted PST: exports include attachments, and some attachment types can spread viruses. Outlook blocks certain types. A PST password mainly discourages accidental access on a shared computer; it does not withstand malicious access. Permutation and Cyclic encoding provide obfuscation rather than reliable encryption.
PST files: open Outlook mail and understand migration limits
Microsoft's specification calls it the Outlook Personal Folders (.pst) File Format. PST has ANSI and Unicode variants with different header layouts: ANSI uses wVer 14 or 15, while Unicode uses wVer 23 or higher.
To transfer Outlook email, contacts and calendar information into a PST, use classic Outlook's PST export. Attachments are included, but folder views, permissions, AutoArchive settings, mail rules and blocked senders are excluded. With Cached Exchange Mode, only currently cached items are exported; check the cache range before exporting.
How to open it
In classic Outlook, choose File → Open & Export → Open Outlook Data File, select the PST, then expand its folders and search for messages. New Outlook can open, read and search PST email, but requires a Microsoft 365 subscription and classic Outlook installed with matching bitness. New Outlook for ARM does not support PST.
In classic Outlook, choose File → Open & Export → Open Outlook Data File, select the PST, then expand its folders and search for messages. New Outlook can open, read and search PST email, but requires a Microsoft 365 subscription and classic Outlook installed with matching bitness. New Outlook for ARM does not support PST.
To transfer Outlook email, contacts and calendar information into a PST, use classic Outlook's PST export. Attachments are included, but folder views, permissions, AutoArchive settings, mail rules and blocked senders are excluded. With Cached Exchange Mode, only currently cached items are exported; check the cache range before exporting.
File safety
Assess attachments separately when handling an untrusted PST: exports include attachments, and some attachment types can spread viruses. Outlook blocks certain types. A PST password mainly discourages accidental access on a shared computer; it does not withstand malicious access. Permutation and Cyclic encoding provide obfuscation rather than reliable encryption.
An unknown sender, a name ending in two extensions, or contents that do not match the extension — check before you open it.
Converting it
To transfer Outlook email, contacts and calendar information into a PST, use classic Outlook's PST export. Attachments are included, but folder views, permissions, AutoArchive settings, mail rules and blocked senders are excluded. With Cached Exchange Mode, only currently cached items are exported; check the cache range before exporting.
Convert a copy, never the original, then compare quality, metadata, and layout against what you started with.
Common questions
What is a PST file used for?
A PST stores Outlook email, contacts and calendar information and can be used to transfer that information.
How do I open a PST file in classic Outlook on Windows?
Choose File → Open & Export → Open Outlook Data File, select the PST, then expand its folders to browse or search messages.
What are the requirements for opening PST email in new Outlook?
New Outlook requires a Microsoft 365 subscription and an installation of classic Outlook with matching bitness. It can open, read and search PST email.
Why can't new Outlook for ARM open my PST file?
Microsoft states that new Outlook for ARM does not support PST. The documented opening procedure uses classic Outlook.
PST ANSI vs Unicode: how do the formats differ?
Their header layouts differ. The specification identifies ANSI with wVer 14 or 15 and Unicode with wVer 23 or higher.
How do I export Outlook email to PST, and which settings are lost?
Use PST export in classic Outlook. It includes attachments, but excludes folder views, permissions, AutoArchive settings, mail rules and the blocked senders list.
Why are emails missing from my PST export?
With Cached Exchange Mode, Outlook exports only items currently in the cache. Check whether the missing messages fall outside the cache range.
Can attachments in a PST file carry viruses?
Yes. PST exports retain attachments, and Microsoft warns that some attachment types can spread viruses. Assess untrusted attachments separately; this does not mean the PST itself automatically executes code.
What are the limits of PST password protection?
A PST password mainly helps prevent accidental access on shared computers and does not resist malicious access. Individual folders cannot have separate PST passwords.
Does PST file header validation prove that the file is safe?
No. The !BDN marker at offset 0 and SM at offset 8 help identify the format and should be checked with version fields. They do not establish attachment safety or content trustworthiness.
Related formats
Sources
[MS-PST]: HEADER · Microsoft 官方格式规范
Open and find items in an Outlook Data File (.pst) · Microsoft 官方支持
Export emails, contacts, and calendar items to Outlook using a .pst file · Microsoft 官方支持
Set a password to help protect your Outlook information · Microsoft 官方支持
[MS-PST] Outlook Personal Folders (.pst) File Format, 2022-02-15, §4 Security Considerations · Microsoft 官方格式规范
Blocked attachments in Outlook · Microsoft 官方支持