What RFC number defines the DKIM standard?

RFC 6376 defines the DomainKeys Identified Mail (DKIM) signature standard. Published by the Internet Engineering Task Force in September 2011, it became the principal standards-track specification for signing email with a domain-linked cryptographic signature.

DKIM lets a sending organization assert responsibility for a message. A mail server signs selected headers and the message body with a private key. The receiving system uses the domain and selector in the DKIM-Signature header to locate the matching public key in DNS, typically beneath the _domainkey namespace.

RFC 6376 replaced earlier DKIM specifications, including RFC 4871 and RFC 5672. It does not encrypt email; instead, it helps receivers detect tampering and assess whether a message was authorized by the signing domain. Later RFCs update parts of the specification, including cryptographic algorithms and operational guidance, but RFC 6376 remains the canonical RFC answer to this quiz question. The distractors refer to related email standards: RFC 7208 defines SPF, RFC 7489 describes DMARC, and RFC 5321 defines SMTP.