DKIM is claimed to be an upgrade of Yahoos DomainKeys. What is different and why should I upgrade?
DKIM is the result of a multi-company effort to enhance DomainKeys for broader adoption, better security, and more flexibility. NOTE: DKIM is upward compatible with existing DomainKeys DNS records, so that a DKIM module does not automatically require additional DNS administration! A lengthy list of the technical differences is in the Comparisons section, below.