SPF, DKIM and DMARC are difficult to configure and require careful study to understand how they inter-relate and complement each other with their protective features. SPF hardens DNS servers and restricts who can send emails from your domain. DKIM ensures that the content of your emails remains trusted and hasnt been tampered with or compromised. DMARC ties the first two protocols together with a consistent set of policies. The effort, however, is worth the investment in learning how to use them.”]
Source: https://www.csoonline.com/article/3254234/mastering-email-security-with-dmarc-spf-and-dkim.html