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. It uses the same binary structure as PST (magic bytes "!BDN") and lets Outlook work offline. OST to PST conversion takes that offline cache and repackages the extracted content into a PST-style structure — Outlook's standard data file format — so you can back up or migrate Exchange cache when the account is no longer accessible or when moving to another PC.

Our free OST to PST converter processes entirely on your device. You drop a .ost file, and the tool validates the header, scans for email-like content, then builds a PST-style export from the extracted messages. All processing is private; nothing is uploaded. For a native PST that Outlook opens with full fidelity, a dedicated desktop OST-to-PST tool may be needed; our export is ideal for backup and for converting onward to EML, MBOX, or other formats.

Common use cases include recovering data when an Exchange account is disconnected, migrating Outlook/Exchange mail to another computer, and creating a backup in a format that aligns with PST. 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 PST-style makes the data usable in backup and migration workflows.

For 100% fidelity and a PST that Outlook opens directly, use Outlook or a dedicated desktop OST-to-PST converter. This tool extracts as much as possible on your device and is ideal when you don't have Outlook or when you need a quick backup or intermediate format.