DomainKeys Identified Mail
DomainKeys Identified Mail (DKIM) is an email authentication method that permits a person, role, or organization that owns the signing domain to claim some responsibility for a message by associating the domain with the message. The receiver can check that an email that claimed to have come from a specific domain was indeed authorized by the owner of that domain.
Source: Wikipedia — DomainKeys Identified Mail (CC BY-SA 4.0)