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 HTML conversion takes that offline cache and exports each email as HTML — the same format used by web pages, so you can open messages on any device without an email client.

Our free OST to HTML 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), then generates HTML output for each message. All processing is private; nothing is uploaded. This lets you turn Exchange/Outlook offline data into viewable web pages on any device.

Common use cases include archiving emails as HTML for long-term storage, sharing a single message by sending the HTML file, and viewing Outlook cache on a machine without Outlook. Because the converter is private, you can use it on any operating system. OST files are typically found on Windows where Outlook has been used with Exchange; converting to HTML makes the content portable and universally viewable.

For full fidelity including all inline images and complex formatting, Outlook or a dedicated desktop OST tool may be needed. This tool extracts as much as possible on your device and is ideal for viewing and archiving when you don't have Outlook available.