If your Exchange Server is down and you want to access OST file emails in a browser format, on the internet, there are multiple sources, but I suggest using
ToolsBaer for OST to HTML Conversion. Because it will help you to access your emails in a browser by converting OST to HTML format. The software comes with multiple features like bulk conversion, preview of mailbox, and has a user-friendly interface, which makes it easy to use, even for novice users. It comes with a demo version, so users can easily understand it without any trouble.