if you have advanced protection on, google will mangle all your emails, even via imap, to rewrite all URLs to the google redirector, breaking email signatures, breaking PGP crypto signatures, et c.
if you want to back up your mail in its original form, you have to do it via data takeout/export.
also google: if you want to export your email unmodified, it takes months(!) because you have advanced protection on.
@sneak something tells me they corrupt the emails at-rest, and need to uncorrupt them first. But even if you want to trust Google to protect you, this "service" is redundant because most browsers support Google Safe Browsing. My theory is that, since they got caught spying with GSB and had to do a less leaky implementation, they decided to snoop people's emails instead.
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