DKIM (DomainKeys Identified Mail) is an email authentication method that attaches a digital signature to outgoing emails to verify the email's authenticity and detect email spoofing. * SPF (Sender Policy Framework): Specifies which mail servers are authorized to send emails for a domain but does not involve digital signatures. * DNS Pointer (PTR): Used for reverse DNS lookups, not email authentication. * MX Records: Specify mail servers for email delivery but do not authenticate emails. CompTIA A+ Exam Reference: Core 2 (220-1102), Section 2.4, email security and authentication.