Each mail folder is represented by a POST log. Each log entry represents a change to the state of the associated folder, such as the addition or deletion of a message. Furthermore, since the log can only be written by its owner and its contents are encrypted, ePOST preserves the expected privacy and integrity semantics of current email systems with storage on trusted servers.
An email insertion record contains the content of the message's MIME header, the message's handle and its decryption key, and a signature of all this information, taken from the sender's original notification message. This data is then encrypted under the user's public key.