DomainKeys is an anti-spam software application in development at Yahoo that uses a form of public key cryptography to authenticate the sender's domain. Today, the sender of a spam message can spoof the originating address so that recipients will think it came from someone else and thus open it as legitimate mail. Yahoo's software would enable the receiving end of e-mail to easily filter out notes in which the sender's stated address could not be authenticated as the actual address. Yahoo plans to make its software freely available to open-source developers, hoping that it will be adopted, installed, and implemented throughout the Internet. In a Reuters interview Brad Garlinghouse, Yahoo's VP of communications products, described the scope of the DomainKeys initiative: "What we're proposing here is to re-engineer the way the Internet works with regard to the authentication of e-mail."
In the Yahoo anti-spam system, an e-mail message would have the originating domain's private key securely embedded in its header term>. When the message arrives at its destination, the key can be compared to the stated domain's public key in the domain name system (digital signatures, and then forges messages using them. However, such problems are not insuperable. Proponents argue that Yahoo has a potential solution to the spam problem in DomainKeys and that, with the ever-increasing glut of spam on the Internet, we should give even possible solutions a good trial before dismissing them.
There are a number of similar spam solutions proposed, including Sender Permitted From (SPF), the Designated Mailers Protocol (DMP), and Reverse Mail Exchange (RMX).