I'll agree that POP is pretty easy and worthwhile here.
One caveat: I'm not certain that it's identical to what Takeout provides. I downloaded the mbox file via Takeout and the Takeout version was a fair bit larger than my Thunderbird mbox file as I recall. Maybe Thunderbird stores the emails more efficiently than Takeout? I should examine this more closely. As far as I am aware there are no missing emails in Thunderbird, though I could write a script to be certain.
Edit: Seems that I misremembered. The Takeout file seems to be appreciably smaller than what Thunderbird has, but in line with what Gmail reports at the bottom. I guess Thunderbird is actually less efficient than Gmail. Attachments might explain some of this, as I deleted some attachments in Gmail that I kept in Thunderbird.
Yes, it was zipped, but I was comparing uncompressed. I've now checked. There's about a 500 MB difference for about 10 GB of emails. So not too bad, but appreciably different.
