Which of the following is the BEST way to ensure email confidentiality in transit?

Complex user passwords protect access to the email client or mailbox, but they do not secure the email content itself while it is in transit across networks.

Digital signatures provide authenticity and integrity by verifying the sender's identity and confirming the message has not been tampered with, but they do not encrypt the message content for confidentiality.

End-to-end encryption ensures that email content is encrypted at the sender's client and remains encrypted until it reaches the intended recipient's client, preventing unauthorized interception and viewing of the message by intermediate servers or entities. This method guarantees confidentiality throughout the entire transmission path, even if the network segments are otherwise insecure.

Encryption of corporate network traffic protects email only while it is within the encrypted network segment or between specific servers, but not necessarily from the sender's client to the recipient's client across all potential hops.