DomainKeys Identified Mail Signatures v2 (DKIM2)

DomainKeys Identified Mail v2 (DKIM2) permits a person, role, or organization that owns a signing domain to document that it has handled an email message by associating their domain with the message. This is achieved by providing a hash value that has been calculated on the current contents of the message and then applying a cryptographic signature that covers the hash values and other details about the transmission of the message. Verification is performed by querying an entry within the signing domain's DNS space to retrieve an appropriate public key. As a message is transferred from author to recipient systems that alter the body or header fields will provide details of their changes and calculate new hash values. Further signatures will be added to provide a validatable "chain". This permits validators to identify the nature of changes made by intermediaries and apply a reputation to the systems that made changed. DKIM2 also allows recipients to detect when messages have been unexpectedly "replayed" and will ensure that Delivery Status Notifications are only sent to entities that were involved in the transmission of a message.