• How To Implement Domainkeys In Postfix Using dk-milter
  Domainkeys is "a method of e-mail authentication. Unlike some other methods, it offers almost end-to-end integrity from a signing to a verifying Mail Transfer Agent (MTA). In most cases the signing MTA acts on behalf of the sender, and the verifying MTA on behalf of the receiver. DomainKeys is specified in Historic RFC 4870, which is obsoleted by Standards Track RFC 4871, DomainKeys Identified Mail (DKIM) Signatures." according to the wikipedia. So why a how to on it when there is DKIM? Well domainkeys is still actively being used and is more widely deployed than DKIM, the developer Yahoo still uses it to sign and verify mail although they are contributers to the DKIM standard.
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