DKIM and DMARC are often mentioned together, but they operate at different layers. DKIM cryptographically signs your messages so receivers can verify they weren't altered and came from your domain. DMARC sits on top, telling receivers how to handle mail that fails authentication and where to send reports.
DKIM is a mechanism; DMARC is a policy. Without DMARC, a DKIM failure has no defined consequence. Without DKIM (or SPF), DMARC has nothing to enforce. They're layers of the same defense.
| Aspect | DKIM | DMARC |
|---|---|---|
| Role | Signs and verifies messages | Sets policy for failures |
| Layer | Authentication mechanism | Enforcement and reporting |
| Depends on | Nothing else to function | SPF and/or DKIM with alignment |
| Output | Pass/fail signature check | none / quarantine / reject action |
| Reporting | None built in | Aggregate and forensic reports |
Set up DKIM (and SPF) first, then layer DMARC on top to enforce and monitor. Start DMARC at p=none to collect reports without affecting delivery, review who's sending as your domain, and gradually move to quarantine and then reject once legitimate sources are aligned. DKIM does the verifying; DMARC turns that verification into action and insight.
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