Email system security should ensure that:

The correct answer encompasses multiple essential aspects of email system security. Each aspect plays a crucial role in safeguarding the integrity, confidentiality, and authenticity of email communications.

First, encryption of messages helps protect sensitive information from unauthorized access. This means that even if a message is intercepted during transmission, it cannot be easily read by an external party. Encryption is a fundamental security measure that ensures personal and confidential data remain secure.

Second, ensuring that messages are complete addresses the need for data integrity. This means that the messages sent are received in their entirety and have not been altered in any way during transmission. Data integrity ensures that the information remains unchanged from the sender to the recipient, which is essential for accurate communication.

Third, the capability to prevent messages from being tampered with adds another layer of security. This aspect involves implementing mechanisms to detect if a message has been altered after being sent. It provides confidence to both senders and recipients that the communicated information is trustworthy and has not been compromised.

Therefore, the most comprehensive answer is that email system security should ensure that messages are encrypted, complete, and cannot be tampered with, which collectively addresses the multifaceted nature of email security.