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What SPF, DKIM, and DMARC actually check
Email uses several identities, and the checks do not all examine the same one.
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- Visible sender: The domain in the message’s RFC5322.From header—the address a reader typically sees, such as
[email protected]. - SPF identity: SPF checks whether a sending host is authorized for the SMTP HELO or MAIL FROM identity. MAIL FROM is commonly associated with a bounce or return-path domain; it is not necessarily the visible From domain. RFC 7208 defines SPF’s scope as the HELO and MAIL FROM identities.
- DKIM identity: DKIM verifies a message signature associated with a signing domain, shown as
d=in a validating signature. That signing domain need not be the visible From domain. - DMARC result: DMARC compares the visible From domain with the authenticated SPF and DKIM identities. It passes if SPF passes and its identity aligns, or if DKIM passes and its signing domain aligns. Either aligned mechanism is sufficient; both do not need to pass.
These distinctions are defined in RFC 7208 (April 2014) and RFC 7489 (March 2015). RFC 7489 explains why alignment matters: a message can have a valid signature from a domain unrelated to the visible sender.
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How valid checks can still fail DMARC
Suppose a message displays From: [email protected]. Its SPF check passes for bounce.vendor.net, and its DKIM signature validates with d=vendor.net. Those results can both be valid: they establish authorization for the sending identity and a valid signature from the vendor’s domain. But neither identity aligns with example.com, so neither supplies the aligned pass DMARC needs.
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This is an illustrative example, not a test of a particular mail service. A provider may instead configure a customer-specific return-path or DKIM signing domain that aligns with the customer’s domain. In that case, the corresponding SPF or DKIM result can satisfy DMARC.
What alignment means
DMARC alignment can be relaxed or strict, and the choice is evaluated separately for SPF and DKIM. With relaxed alignment, domains that share the same organizational domain can align. With strict alignment, the authenticated domain must exactly match the visible From domain. For example, whether mail.example.com aligns with example.com depends on the relevant mechanism’s alignment mode.
Do not infer alignment from a status label that says only “SPF pass” or “DKIM pass.” Check the specific domains the receiver evaluated and the applicable alignment mode.
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How to diagnose a message that appears spoofed
- Find the visible From domain. Read the domain in the message’s RFC5322.From header. This is the domain DMARC evaluates.
- Check the SPF-authenticated identity. In the authentication results for the received message, identify the SPF result and the domain used for the SMTP MAIL FROM identity. A passing result for a bounce domain is not automatically a pass for the visible From domain.
- Check each validating DKIM signature. Identify the
d=domain for every signature that validates. A message can carry multiple signatures; look for a valid one whose domain aligns with the visible From domain. - Evaluate alignment. Apply the strict or relaxed mode for SPF and DKIM separately. DMARC needs at least one passing mechanism whose authenticated domain aligns.
- Inspect the effective DMARC policy. Check the policy published for the visible From domain and whether a subdomain policy applies. Then interpret the receiver’s reported disposition in that context; the DNS policy is not itself a record of what every receiver did.
If neither a passing SPF identity nor a validating DKIM signing domain aligns, the message does not satisfy DMARC even if one or both underlying checks pass.
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What a DMARC policy can—and cannot—guarantee
A DMARC record tells receivers what handling the domain owner requests for messages that fail DMARC. p=none requests no specific action on failures; quarantine and reject request stronger dispositions. These policies are receiver-applied, not a sender-side firewall, and they do not guarantee identical handling by every mail system.
RFC 7489 says receivers should make a best-effort attempt to follow the requested policy, while allowing them to deviate in some circumstances and report a reason. A message may therefore be treated differently by different receivers, or handled differently during complex mail flows. A policy can guide processing, but it cannot make an unaligned SPF or DKIM result become a DMARC pass.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why valid DNS records do not prove every message is protected
A published SPF, DKIM, or DMARC record is only part of the picture. The records must describe the identities used by your legitimate mail flows, and messages need to be evaluated against those identities. A sender can also put your domain in the visible From field without using an aligned SPF or DKIM identity; a receiver’s DMARC evaluation is what determines whether the message passes DMARC, while the receiver decides how to handle a failure.
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