I once had an OST file from an old office laptop, but Outlook was no longer installed on my new system. I assumed the file was useless. After some research, I learned that OST files can still be converted without Outlook using specialized software like the Sysinfo OST to PST Converter Tool.

The process was surprisingly simple. I opened the software, added the OST file, and within minutes it displayed all the mailbox folders in a tree format. I could preview messages, check attachments, and even apply date filters. Since I wanted to use the data in Outlook again, I selected PST as the output format and completed the conversion.

Later, I also needed copies of certain emails for documentation, so I chose the option to convert OST to PDF. That allowed me to save selected emails in a universally readable format.
Read more: https://www.sysinfotools.com/blog/convert-ost-file-to-pst/