Yes, DKIM/DomainKeys is a hash of the content and some of the message headers of an email, which is added as an additional header. A public key for the domain

Yes, DKIM/DomainKeys is a hash of the content and some of the message headers of an email, which is added as an additional header. A public key for the domain name owner is used to verify the hash was generated (and thus the email sent) by the owner of the domain. Email systems can thus quickly/easily check the validity of the hash when receiving inbound messages and flag or discard messages which lack the header or which fail the test.