MBOX file is used in various user and email clients but doesn't open any email client directly as well it becomes more difficult if you don't have a relevant solution.
in this situation, users can try the MailsDaddy Free MBOX viewer tool and open any MBOX-based email client data like Gmail WebMail Thunderbird Entourage, etc. This powerful solution maintains the folder hierarchy after uploading the data into the software.
it supports all Windows and Outlook versions, as well as users, can upgrade in the pro version and migrate MBOX files into desired mail formats like PST, EML, O365, Live Exchange, etc.