If you ever need a backup of your emails to a portable storage device you will probably get an MBOX file from Gmail via Google Takeout containing all your email. These MBOX files are just like other archive files but these one contains emails and can be opened with Mozilla Thunderbird. In order to start first download Mozilla Thunderbird from here. There are different options for macOS, Windows, Linux choose your OS and download. Once the Download completes launching the setup and installs Thunderbird on your machine.
Launch and Setup Account
Now you need to launch Mozilla Thunderbird and setup your account. On the home screen you will see “Setup your existing Email address”, all you need to do is click cancel
Now another dialog box for integration will appear. Click on skip integration to continue.
Now on the home page click on Feeds. Set and Account Name in the dialog box and click Next.
Point to MBOX file
Now Go to Menu -> Account Settings -> Local Folders. Now under Message Storage Browse the MBOX file. Now a Prompt will appear to restart thunderbird. Once restart completes you can check your emails in Local Folders.
To Remove Account In the Account Settings click on Blogs and Feeds -> Account Actions -> Remove.