DKIM Explained: How Email Digital Signatures Protect Your Domain

TL;DR DKIM (DomainKeys Identified Mail) adds a cryptographic signature to every outgoing email, allowing recipients to verify that the message was authorized by the domain owner and was not tampered with in transit. Defined in RFC 6376, DKIM is the most resilient authentication mechanism in the email stack — unlike SPF, it survives forwarding. This guide details the signing architecture, dissects every tag in the DKIM-Signature header, compares RSA and Ed25519 algorithms, and covers key rotation...