The third-party tool eSoftTools MBOX Viewer for opening mbox files is the free mbox viewer. All email clients that support the. mbox, .mbx, .mbs, and .sbd file formats may use it. Single or many mbox files may be exported to MSG, EML, EMLX, HTML, NSF, Office365, Yahoo, and Gmail. It may also show a live preview of the converted file before it is converted. If you're still not convinced, download the free trial version, which converts the first 25 items from each mbox to other file formats.
Read More:- Open MBOX files with MBOX Viewer