Where Are Outlook PST and OST Files Stored?
Classic and new Outlook data file paths on Windows and macOS, and what separates an ost cache from a pst archive.
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An .ost is a local cache of mail that lives on the server. Outlook rebuilds it when you remove and re-add the account, so it is a poor backup, and you cannot open it in another profile or on another machine. A .pst is the portable one: a real file you can move, attach to any profile, and copy to a USB stick.
Which file you have depends on which Outlook you run. Classic Outlook writes both, into two different folders. New Outlook for Windows keeps mail on the server and parks its local state in a folder of its own, so the old AppData path can look empty if that is the app you are using.
Where Microsoft Outlook stores this, by platform
%localappdata%\Microsoft\Outlook (.ost) and %USERPROFILE%\Documents\Outlook Files (.pst)
These are classic Outlook's defaults. OneDrive can redirect Documents, in which case the .pst turns up under OneDrive\Documents\Outlook Files instead, which is common on new machines. New Outlook for Windows uses neither folder: its cache, attachments and IndexedDB data sit in %LOCALAPPDATA%\Microsoft\Olk, with settings under %LOCALAPPDATA%\Packages\Microsoft.OutlookForWindows_8wekyb3d8bbwe. In classic Outlook, File > Account Settings > Account Settings > Data Files lists every file and offers an Open File Location button, which beats typing paths.
~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles/Main Profile
Outlook for Mac does not keep a per-account .ost or .pst. It caches mail as an SQLite database inside this profile folder, and the new Outlook for Mac keeps its cache under the same UBF8T346G9.Office/Outlook group container, with app preferences in ~/Library/Containers/com.microsoft.Outlook. Support for the legacy app ends in October 2026, so most Mac users are already on the new one. Finder hides Library by default, and the Mac app has no Data Files tab, so Go > Go to Folder with this path is the fastest route.
Frequently asked questions
can i open an ost file in another outlook profile
No. An .ost is bound to the mailbox and the profile that created it, and Outlook will refuse to attach it anywhere else. To move that mail somewhere useful, export to a .pst through File > Open & Export > Import/Export, or simply add the account again and let a fresh cache build.
where does new outlook store its data
On Windows, %LOCALAPPDATA%\Microsoft\Olk holds the local cache, attachments and web storage, and %LOCALAPPDATA%\Packages\Microsoft.OutlookForWindows_8wekyb3d8bbwe holds settings. Mail itself stays on the server. Any .pst you add is opened from where it already sits, usually Documents\Outlook Files.
what is the difference between pst and ost
An .ost is a cached copy of server mail: tied to one profile, useless as a backup, and safe to delete because Outlook rebuilds it. A .pst is a standalone archive that can hold mail no server has, which makes it the file worth backing up, moving and guarding.
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