Does Ubuntu have a Large File 3G+ '.mbox' email reader

I recently archived my Gmail that consisted of 46K emails. I downloaded a 3G '.mbox' file from Gmail. I need an '.mbox' reader so I can search and read these emails.

I recently learned the US Gov considers any digital media on the internet that is over 180 days old AS TRASH that they can read legally by any US government department under the US constitution. I immediately wanted to hide my old emails. I've kept them from 2006 when I first started a Gmail account. I have a severe memory disability and keeping these files have saved me from untold trouble by simply searching though old email.

Whether it is constitutional or not is not really my issue. Though I do not believe the Government has the right to read any of my email as though I threw it out in the trash bin on the street. But, I do need to be able to go through my email to find documents, that are old, e.g. with passwords to online accounts, etc. from various sources that I had personal or business dealings with.

I therefore need a tool that can read this Gmail '.mbox' format in a 3G+ sized file. Once I have a working tool I will delete all of my email from Gmail servers. Then I can simply add a new archive and delete the email server every 179 days from this day on.

I've tried Gedit, various browsers, and LibreOffice products etc. But all have a problem with the size of the file and eventually shutdown while trying to load the file.

Thank you for your time, effort, and help.