I suggest the most user-suggested and powerful conversion tool for opening MBOX files in Gmail is known as SysInspire MBOX Converter Software. It supports 25+ email clients of MBOX files such as WebMail, Thunderbird, Netscape, SeaMonkey, Apple Mail, PowerMail, Kmail, Opera Mail, Eudora Mail, and additional email clients and is also workable in Window OS version upto 11. It imports MBOX files in Gmail with email attachments without losing data of MBOX file and the user can also convert MBOX file to other 10+ formats.
Read More: Open MBOX file in Gmail
Read More: Open MBOX file in Gmail