It really is not backed by cryptographic security at all. Since your server has access to plaintext emails when sending and recieving (99.99999% of email addresses would be outside skiff), which completely subverts the whole point of encryption. A vulnerability on the server could leak all user emails, without needing their keys.... This is a solution theoretically only as strong as encryption at rest.
Again, only between users with skiff emails, which is a negligible portion of all emails. This needs to be made clear as it is very misleading to the average user who probably thinks all emails are end to end encrypted.
No: Skiff does not have access to a single email stored on our platform, including ones received externally. All are public-key encrypted, including subjects and content.
This is encryption at rest, with the user holding the keys, and not end to end to end encryption, since the server recieves emails coming outaide of akiff in unencrypted form to begin with.
As a simple demonstration, even if client side code is perfectly secure, an adversary with server control can simply log all emails passing through the server and instantly have access to all new user emails that way. This means users have to trust the server, contradicting any notion of E2EE.
