The Sender Policy Framework (SPF) is a security mechanism created to prevent fraudsters from sending emails on your behalf. This mechanism relies on communication between DNS servers. The DomainKeys Identified Mail (DKIM) standard was created for the same reason as SPF: to prevent fraudsters from impersonating you as the sender of an email. It is a way of additionally signing your emails, so that the recipient's server can verify whether the sender was really you or not. By setting DKIM in DNS, you add an extra way to tell recipients "yes, it's really me sending this message”.