These three standards work together but check different things, and all three are generally recommended for proper email authentication.
Side-by-side
- SPF: checks whether the sending server is authorized for the domain
- DKIM: checks whether the message content is authentic and unaltered, via a cryptographic signature
- DMARC: checks that SPF and/or DKIM align with the visible "From" domain, and tells receivers what to do (none/quarantine/reject) if they don’t — plus provides reporting
Why you need all three
SPF alone breaks on simple email forwarding; DKIM alone doesn’t stop a spoofed "From" address if the attacker uses their own valid DKIM signature on a different domain; DMARC ties both together and is what actually lets receiving servers reject a spoofed message with confidence.
FAQ
Is DMARC useless without SPF and DKIM already set up?
Yes — DMARC evaluates SPF and DKIM results, so it has nothing to enforce against if neither is configured.