How to Use DKIM to Prevent Domain Spoofing - SendGrid https://sendgrid.com/blog/how-to-use-dkim-to-prevent-domain-spoofing/
Neither SPF or DKIM fully secure an email. Each is missing an important piece. SPF is missing message verification and DKIM is missing a way to verify where the message is coming from. Both are needed to be a secure email sender.