What does DKIM use to ensure each email is trustworthy?

DKIM, or DomainKeys Identified Mail, utilizes encryption keys and digital signatures to validate the authenticity of email messages. This technology helps to ensure that the email content has not been altered during transmission and confirms that the message originated from the designated sender's domain.

When an email is sent, DKIM generates a unique digital signature using a private encryption key, which is added to the message headers. The recipient's email server can then use the corresponding public key, published in the sender’s DNS records, to verify the signature. If the signature matches and the email remains unaltered, the receiving server can trust that the email is authentic and legitimate.

Based on this process, it is clear that DKIM relies heavily on encryption keys and digital signatures to secure the email's integrity and authenticity, making this the correct answer. Other options do not relate to DKIM's functioning; for instance, usernames and passwords are more associated with user authentication rather than email verification, and authenticator apps relate to multi-factor authentication rather than email security. Advanced cloaking technology is unrelated to email transmission security features.