DomainKeys Identified Mail (DKIM)
A DKIM signature is added to the header field of every email that is sent out. This unique signature captures the inputs required by the receiving server to authenticate an email.
The DKIM signature holds vital information about the cryptographic signature, body hash, and details on where the Public Key can be retrieved by the receiving SMTP server. DKIM uses public or private key cryptography for the verification process. A Public Key is a TXT record published in the DNS manager. The signer uses the private key and the verifier uses the corresponding public key to complete the process of email authentication.