> All without needing to keep the data downloaded on your device, and backed up in the cloud.

I'd call this a feature of email – I _can_ easily have all the stuff I need downloaded on my device. I can move email around without using a specific provider, back it up to an offline storage just like any other data, and use multiple clients without re-syncing all the emails.

Also it's perfectly possible to have email available over the Internet, only downloading things to your device when needed. Most modern email services work this way – either through webmail and/or using email protocols like IMAP.

(That's not to say that email is perfect. Far from. The content of email is a hot mess – broken HTML implementations, HTML email trying to do ungodly things, plaintext with hard line breaks, plaintext displayed with no line breaks whatsoever, RTF...)