The inverted index could simply be built/live on client side. The cloud is then just a backup data storage. Encrypted email is downloaded, unencrypted and indexed on your laptop/phone etc.
To be clear, you're proposing that users download their entire email storage to their phones and browsers before they can search or spam filter their email? And you think that this would be a compelling product for the average email user? I'm having a hard time figuring out if you're trolling.
Isn't this how pretty much any mail client does it? Thunderbird does a decent job at spam filtering my mail. You know, I can even search folders in Outlook! Saying that scanning your 1M mails with 1kb each requires the use of a cloud service seems a bit over the top.
And how long does that search take? How long does it take to download that mail to a new device? How long would that have been on 2006 Internet? I've never said that it's impossible. I've only said that it takes away the main advantage claimed at launch — fast, working search.
Sure - might not be easy for email. It does work for imessages (no server storage, typical size 1-5GB, stored + indexed on client side). So once phones start having 50GB+ storage(wait my iphone already does :p), its not so far fetched to think of having a 20GB inbox stored+indexed on the phone - of course you don't need to store the attachments etc.
Anyways, my point was not to suggest a full solution but to say that companies are not incentivized to solve this problem.
> its not so far fetched to think of having a 20GB inbox stored+indexed on the phone
Yes it is. Besides just syncing the data there are a huge number of other performance hits.
> of course you don't need to store the attachments etc.
Why not? Do you want to a) drop support for searching through attachments (like pdfs) or b) not encrypt those?
> companies are not incentivized to solve this problem.
There has been huge improvements in the last few years in this space (take Signal as an example). But major email providers are not incentivized because most users don't care, UX and performance suffer, email is inherently an unsafe (even if you put PGP on top [1]) and because they would not be able to make as much ad revenue (worse targeting).
A huge number of emails plus attachments are large in size. It is that controversial because it is hard to make it perform on a mobile device over a crappy 3g connection.
To be fair, mobile clients WOULDN'T download the entire email catalog for local search. It gets up to X days locally and the rest will be searched online. But you are right though, you really can't build the index remotely of you want end-to-end encryption.
You don't need to store the data locally, you can just store indexes and filters. Keep them up to date in an online fashion and the cost is a fraction of the storage space required, and some extra CPU time spend locally.