In my previous article, I spoke about DKIM and how to implement it with Postfix by using dkim-milter. In this article, we’ll be talking about DomainKeys which is confused with DKIM almost every time. Then we’ll be implementing it with Postfix by dk-milter on a FreeBSD box.
Both of these PGP-like methodologies are used for aiding the same ultimate purpose, the sender authentication, with slight differences in practice. When it comes to functionality, both are providing more effective validation mechanism over the source when compared to a single SPF record which is an earlier de facto standard.
DKIM is a sender authentication scheme for signing messages in a way that these messages can be validated by the recipient side. DKIM, which is usually a part of MTA, is based on public-key cryptography therefore the validation process naturally depends on public-private key pair. Signer MTA affixes a digital signature into the message header by “DKIM Signature:” field which will then be used by the verifier side to recover the signer’s public key via DNS and complete the verification.
