Outlook Offline Archive

OST Viewer

Access and search Outlook OST offline storage files, without a working Outlook connection. Upload your OST archive and find any message instantly.

Upload OST file →

What is an OST file?

An OST (Offline Storage Table) file is created by Microsoft Outlook to store a local copy of your Exchange or Microsoft 365 mailbox. Unlike PST files, OST files are tied to the Exchange account that created them, which makes them notoriously difficult to open once the account no longer exists or the Exchange server is gone. OST files are commonly encountered during IT migrations, employee offboarding, and when recovering email from a decommissioned server.

Evermail + OST

How Evermail handles OST files

Upload once. Search forever. No conversion, no special software needed.

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Upload your OST file

Upload the OST file directly to Evermail. No Exchange server connection needed, no Outlook installation required.

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Parsing & indexing

Evermail reads the OST file format natively, extracting all messages, folders, calendar items, and metadata for full-text indexing.

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Search and export

Search across all indexed content with fast full-text search. Export messages as EML or MBOX for archiving or migration.

Why Evermail

Key features for OST archives

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No Exchange server needed

Access OST content without a live Exchange connection or matching user account. Perfect for orphaned mailboxes after migrations.

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AI-assisted summaries

Generate concise summaries of long emails and threads, so you can review an orphaned mailbox faster.

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Complete folder structure

Inbox, Sent Items, Deleted Items, Calendar, and custom folders are all preserved and browsable exactly as the original mailbox.

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Export to open formats

Download emails as EML or MBOX. Convert your OST to a standard format for long-term archiving or migration to a new email platform.

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IT migration support

Ideal for IT teams migrating from Exchange to Microsoft 365, Google Workspace, or any other platform. Bulk OST archiving on Team and Enterprise plans.

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GDPR-compliant processing

All OST data is processed in EU data centres. Choose from three security levels, including a Confidential mode that encrypts content at rest under your own key (BYOK).

Open your OST archive today

No special software. No conversion. Upload, index, and search. Free to start.

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FAQ

Common questions about OST files

What's the difference between PST and OST files?
PST is a standalone archive file you create manually in Outlook. OST is automatically created by Outlook to cache your Exchange/365 mailbox locally for offline access. OST files are tied to the account that created them, while PST files are portable.
Can I open an OST file without the original Outlook account?
Yes. Evermail reads OST files directly without requiring the original Exchange account, active server connection, or even an Outlook installation.
My OST file is from a deleted user account. Can Evermail still read it?
Yes. Evermail reads OST files at the file level, independently of any Exchange account. This makes it ideal for recovering email from offboarded employees or decommissioned servers.
Can I convert an OST file to PST or MBOX using Evermail?
Evermail lets you export individual emails or folders as EML or MBOX files. For PST conversion, we recommend importing the exported MBOX file into Outlook.
What if my organization has disabled email export in Outlook?
If your IT admin has turned off Outlook's export options, you can still export your live mailbox over IMAP using Thunderbird, or Apple Mail on a Mac, and upload the resulting file. See our step-by-step guides at evermail.ai/guides/export-outlook-windows (Windows) and evermail.ai/guides/export-outlook-mac (macOS).
Is my data safe with Evermail?
Yes. Evermail is EU-hosted and GDPR compliant. Your emails are stored on Azure EU infrastructure and never leave the EU. You can choose from three security levels per mailbox, including client-side zero-access encryption.
How much does it cost?
Evermail has a free plan (1 GB, 30-day retention) to get started at no cost. Paid plans start from €4.99/month for 5 GB with permanent retention. See full pricing →