The most simple way to convert a large number of files at once without losing data is to use the PST to MBOX Converter application. eSoftTools Software, filters, and configures only the data you specify. During the migration, email items and other data are preserved. The folder and subfolder structure will stay unchanged during and after the migration. There is a free trial version to try out! It allows you to evaluate all of the capabilities without restriction, also unlimited pst file conversions. It is not required that you have any technical knowledge to use this software.