2007/06/04 DomainKeys が Historic RFC となりました(RFC4870)。それに代わり、DKIM が Proposed Standard RFC となりました(RFC4871)。(2007/05)
4871 DomainKeys Identified Mail (DKIM) Signatures http://www.rfc-editor.org/rfc/rfc4871.txt
4870 Domain-Based Email Authentication Using Public Keys Advertised in the DNS (DomainKeys) http://www.rfc-editor.org/rfc/rfc4870.txt