EML files are basically an offline format of your daily emails. This will convert in bulk and singly. To convert EML files into MBOX file format, you can use Advik EML to MBOX Converter. This is simple to use and easy to install on any Windows OS. This tool maintains data integrity and generates a final report of converted files. This is a fully safe and easy-to-use wizard. I used this program multiple times and got the best result.