The email migration is a very lengthy and complex process, and it becomes so frustrated when you have numerous emails for conversion, and you have to convert them one by one manually. I would highly recommend BetaVare EML to MBOX Exporter as it provides a lot of features that simplify and shorten the conversion process. It provides bulk conversion, which allows users to convert multiple files at once and saves users a lot of time and effort. It converts emails securely without any data loss, which makes it more reliable. I think you should go for this without wasting your time.
For more information: https://www.betavare.com/eml/mbox/