I've recently set an offline mail client to sync mail locally for my wife's laptop. Her two gmail accounts downloaded 22GB.
Be careful what offline actually means when it comes to mail; eg. that 22GB as service worker cache sounds a bit nasty to me, especially because service workers don't tend to differentiate between desktop and mobile.
Definitely. I’d hate to have it download all my mail on my laptop or my phone. We have yet to particularly consider the UI for controlling it, but I fully expect that anything in the way of synchronisation rather than simple caching of what we’re already fetching (and only limited amounts of that—there’s already an LRU GC on the cache) will require manual configuration, probably with options like “sync the inbox” or “sync the last 30 days of mail”, and probably projections of probable storage requirements.
If you want a local backup of all your mail, using a web app like ours, even if it supports fetching it all, is not a good idea, unless it satisfies both of these criteria:
(a) it should support fully offline and session-agnostic functionality. We’re very unlikely to ever go this way on fastmail.com, because it’s just not going to be useful to almost anyone, and is more complex and easily leads to confusion. Instead, the data will be tied to your session, so that if you log out, or your session is permitted to expire, or you close your account, then the data will all promptly be deleted when you next go online.
(b) it has a way to export it again. Theoretically with JMAP we could actually do that, but even if we did implement it (and I doubt we ever will), it lacks the portability of other formats like mbox or PST.
Taking both of these points together, I say that an email service provider’s app’s sync should not be considered suitable for a backup. For convenient offline access, perhaps, but not for a backup.
Why would anyone that has that amount of mail go out of their way to get a phone with such limited capacity. At this point a phone with 16gb serves the purpose of being a burner phone.
There is no limit on gmail. For someone who has it for a decade or more, 20GB mail is realistic, since gmail always told you there is no need to delete anything, ever.
As for 16GB phones, those are pretty normal; take a look at moto e5. Please don't tell me a 64GB phone is required for email.
It also doesn't change the initial problem of what and how much should be cached by service workers.
Be careful what offline actually means when it comes to mail; eg. that 22GB as service worker cache sounds a bit nasty to me, especially because service workers don't tend to differentiate between desktop and mobile.