I save important official docs from my mail — I even sometimes export eml files to those archive/backup folders. So all those get backed up.

The emails themselves? Not really — even though the mail folder (Thunderbird’s; not Mail.app’s — can’t trust an Apple made utility app to be part of even a half hearted backup process) is actually part my backup routine as part of one of those 3 backup tools running on my system (and 2 sync tools). But I seriously doubt I am going to find an email from a backup snapshot ever. But if I must I have that.

But I would want to — have wanted to. Maybe a dedicated tool that downloads every single mail and keeps it synced with the server in an email file format that’s most efficient for backup and querying that backup later. Or maybe tweak around Thunderbird that makes that happen.

Edit: Oh, I forgot to mention — I immediately delete those official mails (like statements, bills) immediately after saving those PDFs if I have to. I think I delete 99% of email I receive (okay maybe 80-90% - not sure; you get the idea). Only personal emails are what I never delete. So I never have too much email to begin with. I do the same with photos and videos and screenshots taken - if it can be detected, it will be deleted.