Your e-mail provider protects your messages (sent/received) from eavesdroppers, using encryption. It applies the latest technologies available, assuring the identity of the parties with which interacts.
Your email provider offers a minimum protection against email spoofing. It will be able to detect some not legitimate email servers and provide a minimum protection against impersonation attempts on its users. This score can also reflect a deployment-in-progress of the required technologies to provide protection against phishing and identity theft.
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.