Answer:
A. The most secure email message authenticity and confidentiality is provided by signing the message using the sender’s public key and encrypting the message using the receiver’s private key
Step-by-step explanation:
Public key cryptography helps to send public key in an open and an insecure channel as having a friend's public key helps to encrypt messages to them.
The private key helps to decrypt messages encrypted to you by the other person.
The most secure email message authenticity and confidentiality is provided by signing the message using the sender’s public key and encrypting the message using the receiver’s private key