This is a reminder of the danger of trusting our data to 3rd parties and who actually is in control of it.
I was in the same situation last week - I needed an old file that was inside a .rar archive, and gmail wouldn't let me download it. I knew about google takeout, but i didn't wat to download several gigs just for that one file, so this is what i ended up doing:
1) In Gmail, create a label (any name will do, like "rar export");
2) Add the message google won't let you download attachments from to this label;
3) Go to google.com/settings/takeout, and look for the option which lets you export a single label from Gmail.
Hope it helps :)
Does IMAP allow you access?
What about google.com/takeout?
Not really. It's a reminder that you should keep backups and test them. If your only copy is in gmail, you don't have a backup.
Another solution is to simply change executable names to .exe.backup or something similar, that way it'll register as a ".backup" extension for most systems and not be blocked simply by name (though this wouldn't necessarily defeat things that actually detect and block binary executables).
Check the box to encrypt file names and they can't scan inside rars.