When you are searching to import/convert EML to MBOX use eSoftTools EML to MBOX Converter software because EML maintain your file into local ways but if you are using this tool MBOX It origanised your emails into the each files in one specific folder This Software contain Free demo edition in all 25 emails items of properties on each folders you can store their File Into own choosing location into the  their PC. when you import with this tool so it has ability to 

directly import EML files into MBOX without any prohibition. 

Know more -  Import/convert EML to MBOX