How to view MBOX file

Download Thunderbird

Click Tools > Add-ons

Click on Get Add-ons at the top of the left sidebar 

Search for ImportExportTools NG and install it

1. 1. Accept the terms (see image below)

Click on Tools again, scroll down to ImportExportTools,

Select “Import mbox file.”

Pick option 1) a single .MBOX file or 2) multiple

Find the .MBOX file(s) you downloaded from Google.