Your e-mail provider provides you with a minimum level of confidentiality, using encryption when delivering and receiving messages. Although it cannot assure the identity of the parties with which interacts.
Your email provider cannot distinguish between messages received from legitimates sources from messages received from not legitimate ones (spam and phishing messages are usually sent from not legitimate servers). Moreover, it does not protect against impersonation attempts on its users.
Your email provider cannot guarantee that the messages received were not modified during the delivery phase. In particular, when we have 2 stars we can only guarantee that the message sent from the last server is the same it received. Although it cannot guarantee that it is the same that was sent by the sender.