I just downloaded all my mail from Gmail. I figured it was time to have a copy of all my email here. Especially so the files would show up in desktop searches along with all my other stuff accumulated over 20-plus years. 

It took a couple of days for Google to build the archive, and when it arrived it was 15.5GB, all of it in one file with a .mbox extension. I guess I was surprised. I thought it would be a zip archive of a folder structure with text files and the enclosures in another folder. Now that I think about it, I realize this wouldn't work, if you wanted to switch to another email system with your archive intact. 

BTW, the title of the file is All mail Including Spam and Trash.mbox -- which is all I really know about the file since I haven't opened it yet. 

Now I know that mbox is a standard file format, and I might be able to get it to open in the Mac mail app, but there's reason to think the file is too big, based on this Quora thread. I was looking for a way to export all the files as text files. And found that even for a standard and open format like .mbox, there don't seem to be any good choices.

Ideally there would be a command line app that converts a .mbox file to a folder structure of text files and another for enclosures.

If you have an idea what to do with a .mbox file other than importing it into a desktop mail app, please post a comment here.