As long as your email is on your own domain, is it really worth the effort? Do a Google Takeout on a regular basis and handle if if the (improbable) event occurs. The likelihood of Google purging your data is basically zero.. we have, what, a half dozen confirmed events over the last decade?
Like the idea, but instead of google takeout, I just have Mail.app on my Mac download my whole email history, and then do Time Machine backups of my Mac to my NAS.
If I ever get locked out of my Google account, I’ll flip my domain to a new provider, and be back up in 15 minutes.
IMO it's less about having an archive; more about being able to receive mail at that address. After all, email address is the root of your identity for basically everything on the web -- what's the plan if every account you have is @gmail.com and Google banishes you? Running it through your own domain means you just re-point it at a different provider and keep trucking.
