Yahoo has finally released its specification for its DomainKeys email authentication scheme. Included is the following patent license (emphasis added):
Yahoo! will grant a royalty-free, worldwide, non-exclusive license under any Yahoo! patent claims that are essential to implement or use any Implementations so that licensees can make, use, sell, offer for sale, import, or yodel Implementations; provided that the licensee agrees not to assert against Yahoo!, or any other Yahoo! licensees of Implementations, any patent claims of licensee that are essential to implement or use any Implementations.