What’s the difference between DKIM and SPF and why does it matter?

Quick Takeaways

• SPF validates the sending server’s IP (Return‑Path), while DKIM validates the message content.
• SPF can fail on forwarded emails; DKIM survives most forwarding unless the content changes.
• DMARC ties SPF and DKIM to the visible From address, improving deliverability.
• Major providers (Gmail, Yahoo, Microsoft) now require both SPF and DKIM for bulk senders.
• Use Palisade’s tools to check SPF, DKIM, DMARC and BIMI status instantly.

What is SPF?

SPF (Sender Policy Framework) is a path‑based authentication method that checks whether the sending server’s IP address is authorized to use the domain in the Return‑Path header. Domain owners publish an SPF record in DNS listing permitted servers, and receiving servers verify the source against that list.

What is DKIM?

DKIM (DomainKeys Identified Mail) signs outgoing messages with a cryptographic hash linked to a private key. The signature is added to a DKIM‑Signature header, allowing the receiver to verify the message’s integrity and confirm the signing domain.

Why use both SPF and DKIM?

SPF and DKIM protect different parts of an email. SPF stops unauthorized servers from using your domain in the envelope, while DKIM ensures the content hasn’t been tampered with. Using both provides layered defense against spoofing and improves inbox placement.

What is the forwarding problem with SPF?

When an email is forwarded, the original Return‑Path remains unchanged, but the forwarding server isn’t listed in the sender’s SPF record. This causes SPF validation to fail, potentially rejecting legitimate messages.

How does DKIM handle forwarding?

Because DKIM validates the message content rather than the path, the signature remains valid through most forwarders as long as the content isn’t altered. However, mailing‑list footers or subject changes can break the signature.

What role does DMARC play?

DMARC (Domain‑Based Message Authentication, Reporting & Conformance) builds on SPF and DKIM by requiring alignment with the visible From address. It lets domain owners set policies (none, quarantine, reject) and receive reports on authentication failures.

How to implement SPF and DKIM step‑by‑step

1. Publish a strict SPF record (use Palisade’s SPF checker to verify).
2. Configure DKIM signing on your outbound mail server (Palisade DKIM tool).
3. Add a DMARC record in “none” mode and monitor reports (Palisade Email Security Score).
4. Adjust SPF/DKIM based on third‑party senders and misalignments.
5. Gradually tighten DMARC policy to quarantine and then reject.

Common questions about SPF and DKIM

• Should I always implement both SPF and DKIM? Yes – major inbox providers require both for bulk mail, and together they provide stronger protection.
• Can SPF or DKIM alone protect my domain? No – each has limitations; SPF fails on forwarding, DKIM can break if content changes.
• How do I know if my records are correct? Use Palisade’s free monitoring tools to scan your DNS and get actionable reports.
• What if I use multiple email services? Publish all authorized sending IPs in SPF and add each service’s DKIM selector to your DNS.
• Is BIMI related to SPF/DKIM? BIMI builds on DMARC, which in turn relies on SPF and DKIM. Check your BIMI status with Palisade BIMI tool.

Additional resources

Explore Palisade’s suite of authentication tools: Email Security Score, SPF Checker, DKIM Analyzer, and BIMI Validator.