There are several free-manual techniques to export EML emails to MBOX format, but they require technical knowledge to do the conversion. I would recommend Softaken EML to MBOX Converter to export emails from EML to MBOX easily, this application can convert all email attributes including cc, bcc, from, topic, date, etc. into MBOX format. It can convert EML files into email clients, including Thunderbird, Apple Mail, Eudora, Sea Monkey, and other MBOX-supported email clients. With just a few mouse clicks users can bulk export EML files. It also offers a preview choice to go over emails before conversion. It is a stand-alone tool, so you do not require another program. You can try its features using its demo version.