DomainKeys Identified Mail (DKIM) is an email authentication standard used to detect email forgery. It is used to verify if an email came from the claimed source or not – aiding in the fight against phishing.
When DKIM is implemented, a digital signature is affixed to each outbound message. The recipient mail server then tries to decode the digital signature using the provided public key. If successfully decoded, the message is authenticated as being from the claimed source.