sentences:  Also, it protects only the content of the email, and not metadata — an untrusted party can still observe who sent an email to whom.A general downside of end to end encryption schemes—where the server does not have decryption keys—is that it makes server side search almost impossible, thus impacting usability.The content of an email can also be end-to-end encrypted by putting it in an encrypted file (using any kind of file encryption tool) and sending that encrypted file as an email attachment.