[bks]

Forwarding emails is problematic especially if your provider for the primary mx does not have great spam filtering and then you end up sending spam to your backup account.

It certainly does not get around the ...if your account gets banned maybe the forwards will still work... concept but in general something like https://github.com/joeyates/imap-backup to backup your email and then add them to a typical backup process with your other files works well.