If you are searching to import/convert EML to MBOX use eSoftTools EML to MBOX Converter software because EML stores your file locally ways but if you are using this tool MBOX converts Your email files into the well format and keeps your data for a longer time. This Software gives a Free demo edition in all 25 email items of properties on each folder you can store their files in a specific location on their PC. when you import with this tool so it is capable of directly importing EML files into MBOX without any prohibition. 

Know more -  Import/convert EML to MBOX