If you are searching for a method to migrate OST files to HTML, then you can use the EmailProHelp OST to PST Conversion Tool. It converts OST files to multiple formats including HTML, MBOX, and PDF. This tool also supports direct migration to Office 365 and other platforms. It handles multiple files at once and offers features like a date filter and duplicate email removal. Compatible with all Windows versions.

More Info: https://www.emailprohelp.com/ost-to-pst-conversion-tool.html