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DKIM

DomainKeys Identified Mail — cryptographic signatures for message integrity.

Reading time:: 5 min
Difficulty:: Intermediate
Estimated duration:: 5 min
Prerequisites:: DNS, CNAME records
Last updated:: 2026-07-15
Author:: empire

Definition

DomainKeys Identified Mail — cryptographic signatures for message integrity.

Prerequisites

DNSDomain Name System — the lookup fabric email authentication depends on.
CNAME recordsDNS aliases often used for DKIM selectors and vendor CNAMEs.

DNSDomain Name System — the lookup fabric email authentication depends on.
CNAME recordsDNS aliases often used for DKIM selectors and vendor CNAMEs.
AuthenticationIdentity signals for email: SPF, DKIM, DMARC, and related controls.
DMARCDomain-based Message Authentication, Reporting, and Conformance.

Broken DKIM key rotationKey rotation leaves selectors unpublished or mismatched.
DKIM body hash mismatchBody modifications invalidate the DKIM body hash.
DKIM key too shortDKIM key length is below accepted operational guidance.
DKIM passes but DMARC failsDKIM validates but signing domain does not align for DMARC.
DKIM public key invalidPublished DKIM key material cannot be used for verification.
DKIM selector not foundThe selector DNS record cannot be located.
DKIM signature missingMessages leave without a verifiable DKIM signature.
DKIM signing-domain mismatchUnexpected d= domain relative to the visible From domain.
DKIM verification failureReceivers cannot validate the DKIM signature.

Mail-TesterSend-a-message spam and authentication scoring for pre-send QA.
DKIMCoreDKIM key and signature oriented validation utilities.

Open step-by-step: Configure DKIMEnable DKIM signing and publish selectors.
Open step-by-step: Migrate authentication recordsMove SPF, DKIM, and DMARC to a new platform without dual-record failures.

Empire Services

SPF, DKIM, and DMARC implementationHands-on implementation of core authentication records and signing.

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