If you are looking for free ways to convert MBOX files into Outlook PST format, I would like to suggest you try the best free manual methods that can easily convert your file format without any interruption. To obtain these free manual methods, read the below-mentioned blog, which contains three manual methods that you can use depending on your version of Exchange Server. This blog's methods is very easy to understand, which is extremely beneficial to all users for file conversion.
To get the blog, visit here: https://www.datarepairtools.com/blog/free-methods-to-convert-edb-to-pst-file/
