Where Does Outlook Store Mail Data Files?
Classic Outlook keeps mail in OST and PST files under %LOCALAPPDATA%\Microsoft\Outlook, with profiles defined in the registry.
Last updated
Classic Outlook splits mail storage by account type, and the file extension tells you which. OST files are cached replicas of Exchange, IMAP, and Outlook.com mailboxes that rebuild from the server. PST files are standalone archives, often the only copy of POP3 mail.
Both live in the same local folder by default, which invites dangerous cleanup. Deleting an OST merely forces a resync; deleting a PST destroys mail. Profiles binding accounts to files sit in the registry, managed through the Mail control panel rather than by hand.
Where Outlook stores this, by platform
%LOCALAPPDATA%\Microsoft\Outlook
OST replicas and PST archives for classic Outlook. OST files rebuild from the server; PST files may be irreplaceable. New Outlook (Store app) keeps data elsewhere, so confirm which Outlook you run first.
HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Profiles
Profile list and account bindings for classic Outlook. Use the Mail applet in Control Panel to manage profiles; hand-editing risks orphaned data files.
Frequently asked questions
Where are mail profiles listed?
Open Control Panel, then Mail, then Show Profiles. The registry key lists configured profiles, but the Mail applet is the supported way to add, remove, and repair them without corrupting entries.
Can I delete OST files to free space?
Yes for POP3, pointless for IMAP and Exchange. OST files are server replicas that rebuild on resync; PST files may be the only copy. Check the account type before treating either as disposable.
Notice an outdated path? Let us know.