For gmail backup, I use https://github.com/gauteh/lieer https://github.com/gauteh/lieer which stores the result in a maildir with labels synchronised with notmu

For gmail backup, I use https://github.com/gauteh/lieer https://github.com/gauteh/lieer which stores the result in a maildir with labels synchronised with notmuch. It uses Google's API to fetch and send e-mails, and is quite performant.