For a secure email service provider, they are very vague about the details. For example, they say there is a second password with which the messages are encrypt

For a secure email service provider, they are very vague about the details. For example, they say there is a second password with which the messages are encrypted and this is only under user's control. Questions: - So how does the receiver decrypts the message? - If user wants to change / rotate their password, does it go back and update the old messages? - Does this second password encrypt your meta data as well?