If you want to open an OST file without using MS Outlook, then you must use one of these tools: Aryson OST Viewer or OST File Opener. Both are the best and most secure OST file reader that can preview all the contents of the OST files, such as emails, events, calendars, contacts, journals, etc. It enables users to open both corrupted and uncorrupted files. The tools are compatible with all versions of Outlook. With these tools, you can convert the OST file data to an HTML file. Tools have many advanced features that make them different. To explore them, you can also use the demo version, which is absolutely free.