The most effective way to accomplish email message authenticity and confidentiality is through using:Sender's private key and encrypting the message using the receiver's public key. Receiver's public key and encrypting the message using the sender's private key. Sender's public key and encrypting the message using the receiver's private key. Receiver's private key and encrypting the message using the sender's public key.

a. Sender's private key and encrypting the message using the receiver's public key.

Explanation:

Email encryption is the encryption and authentication of an email to protect the message therein from being read by any person other than the intended recipients.

It protects the email from hacking or invasion by a third party.

When the message is signed with the sender's private key, the receiver can verify its authenticity using the sender's public key.

Also, encrypting the email message with the receiver's public key provides confidentiality.

Hence, the most effective way to accomplish email message authenticity and confidentiality is through using Sender's private key and encrypting the message using the receiver's public key.