Free OST Converter
Convert to Any Format

OST (Offline Storage Table) is Microsoft Outlook's format for storing a local copy of your mailbox when you use Exchange or certain account types. The file uses the same binary structure as PST (magic bytes "!BDN") and lets Outlook work offline. OST to EML conversion takes that offline cache and exports each email as a separate .eml file — the universal single-message format (RFC 5322) that Outlook, Thunderbird, Apple Mail, and most clients can open.

Our free OST to EML converter processes entirely on your device. You drop a .ost file, and the tool validates the header, scans for email-like content (From:, To:, Subject:, Date:, and body text), then generates one .eml per message. All processing is private; nothing is uploaded. This lets you free your Exchange/Outlook offline data for use in any EML-compatible client or service.

Common use cases include migrating from Outlook to Thunderbird or Apple Mail, backing up Exchange cache as individual EML files, and importing into Gmail or Office 365. Because the converter is private, you can use it on any operating system without installing Outlook. OST files are typically found on Windows where Outlook has been used with Exchange; converting to EML makes the data portable and client-agnostic.

For full fidelity and every last attachment, Outlook or a dedicated desktop OST tool may be needed. This tool extracts as much as possible using private scanning and is ideal for migration and backup when you don't have Outlook available.