Email marketing and web analytics firm CheetahMail announced last week that it is compliant with Yahoo's DomainKeys email authentication specification and is applying the DomainKeys signature to all messaging for domain-managed clients - which its rival Bigfoot Interactive began doing a couple of months ago, reports DM News. CheetahMail is now the largest email service provider to implement DomainKeys; it also complies with SPF and Sender-ID requirements.