If you also have lots of MBOX files and are seeking the right way to import MBOX to Yahoo Mail, then the BitRecover MBOX to Yahoo Converter is the best solution for you. 

It is easy to use, has a free demo edition, allows the desired selection of MBOX files, and migrates the files to Yahoo without any hassle. The best thing is that it is tried, tested, and approved by the industry experts who deal with thousands of MBOX data on a daily basis.