As the authentication wars heat up, with Microsoft's Sender I.D. back in the ring and busting out all over at the Federal Trade Commission's email authentication summit, Earthlink has announced that it is taking Yahoo's Domain Keys out for a spin.

Unlike the other two leading contenders in the email authentication space, Sender I.D. and SPF, both of which focus on the publication of records by the sending email server containing declarations as to the sender's identity, Yahoo's offering works by including in the body of the email a special encrypted key - a digitally encoded signature - which, simply put, matches a key retained on the sending server.

While Domain Keys solves some problems which Sender I.D. and SPF don't (and vice versa), its primary barrier to entry as been that it is somewhat more complicated than the other two, requiring additional steps and resources on the part of ISPs who wish to adopt the technology.

As well as Earthlink's testing of Domain Keys, Gmail is already using it.  In addition, to a greater or lesser degree, all major ISPs have pledged to support all extant authentication schemes.