For brief introduction - Read this Protecting users with SPF, DMARC, DKIM, and MTA-STS
Understanding DKIM - Email Security Series
DKIM is a technological advancement in the field of email security. SPF prevents non-authorized servers from sending emails, but it does not prevent all attempts at spoofing. This is where our next level of security comes into play. DKIM or Domain Keys Identified Mail aids to the security of the email as it adds a digital signature to every outgoing message, allowing receiving servers to verify that the message came from your organization....
