> regular backup of your mail. Google's Takeout service is a straightforward way to achieve this.

Takeout is a horrible way to do regular backups. You have to manualy request it, it takes a long time to generate, manual download... I only use it for monthly full backups.

Much better way for continous incremental backups is IMAP client that locally mirrors incomming emails (Mutt or Thunderbird). It can be configured to store every email in separate file.