DKIM Overview
DKIM stands for DomainKeys Identified Mail and is used for the authentication of an email that’s being sent. Like SPF, DKIM is an open standard for email authentication that is used for DMARC alignment. A DKIM record exists in the DNS, but it is a bit more complicated than SPF. DKIM’s advantage is that it can survive forwarding, which makes it superior to SPF and a foundation for securing your email.
A domain owner adds a DKIM record, which is a modified TXT record, to the DNS records on the sending domain. This TXT record will contain a public key that’s used by receiving mail servers to verify a message’s signature. The key is often provided to you by the organization that is sending your email, for example SendGrid, Postmark, or Google Apps.