Comment by jclulow

This is what I do! The API itself is not particularly amazing (the way it handles batch requests as a MIME multipart formatted POST body where each part is itself a HTTP request is particularly obscene).

The underlying data model is kind of OK though: messages are immutable, they get a long lived unique ID that survives changes to labels, etc. There is a history of changes you can grab incrementally. You can download the full message body that you can then parse as mail, and I save each one into a separate file and then index them in SQLite.