I am searching for a tool that can convert multiple MBOX files without any data loss. I then used SysInfo MBOX Converter Tool that supports bulk conversion and also lets you choose a custom destination path, which helped me store the converted files exactly where I wanted. It also offers to import MBOX files into email clients such as Hotmail, Gmail, Office 365, Thunderbird, IMAP and others. This tool also provides some additional features like using selective email conversion by setting the start and end dates, and to migrate/backup emails without attachments.