In the latest on the continuing sender authentication odyssey, Yahoo! and Cisco just announced they are combining their two separate sender authentication proposals, DomainKeys and Identified Internet Mail, into a single specification, which they plan to propose as a web standard.
The merged technology, called DomainKeys Identified Mail, or DKIM, combines Yahoo!'s method of verifying a sender at the DNS level, with Cisco's approach for maintaining the consistency of header signatures in messages as they traverse networks.
While it's too early to tell, I suspect that Yahoo! will continue to support the original DomainKeys and may even treat it as its primary authentication for the long term. Like it or not, as email marketers, I think we are facing a perpetual alphabet soup of authentication standards.