Addresimg the issue of key availability could be perhaps achieved by OS compatibility. Eg. If two Mac users send each other an email to iCloud addresses it can

Addresimg the issue of key availability could be perhaps achieved by OS compatibility. Eg. If two Mac users send each other an email to iCloud addresses it can be encrypted by default and have iCloud manage the key exchange. This is just a thought on using the cloud as a part the key management similar to what Exchange does. It does not mean that is not hackable since compromising iCloud would compromise both clients but it could be a good start. Encryption by default among same cloud users.