The UIs are terrible. Indexing encrypted email -> difficult. Do it on the server-side and you're essentially storing the email in plaintext on a server -- you

The UIs are terrible. Indexing encrypted email -> difficult. Do it on the server-side and you're essentially storing the email in plaintext on a server -- you might as well have settled for hop-by-hop encryption, which is what MTAs basically try to do anyways. Multiple devices -> yeah, that's tough too. They need the private keys. They need to keep their own indices. End-to-end encrypted email is likely not workable. I'd settle for having hop-by-hop secure email, with a "make it secure" button on send so I can have MTAs bounce when they can't forward securely, and a "secure"/"insecure" label on inbound email that captures whether the whole path inbound was secure or not. Another thing is that end-to-end security in general depends on introducers. CAs, etc. Meaning that the security that users who don't understand these things (99% of users) have in mind is just not what they're ever gonna get in most or all cases.