How does the absence of DKIM affect email deliverability when SPF is passing and DMARC is aligned?
Michael Ko
Co-founder & CEO, Suped
Published 24 Jul 2025
Updated 16 Aug 2025
9 min read
When you're managing email deliverability, you might encounter a scenario where your SPF (Sender Policy Framework) is passing, your DMARC (Domain-based Message Authentication, Reporting, and Conformance) record is aligned, yet there's no DKIM (DomainKeys Identified Mail) signature present on your outgoing emails. The immediate question often arises: Does this absence of DKIM significantly affect email deliverability, or is SPF and DMARC alignment enough?
To clarify, SPF is an email authentication method that specifies which mail servers are authorized to send email on behalf of your domain. DKIM adds a digital signature to your emails, allowing the receiving server to verify that the email hasn't been tampered with in transit and truly originated from your domain. DMARC then ties these two together, telling receiving mail servers what to do if an email fails SPF or DKIM, and providing reports on authentication results.
While DMARC can technically pass if either SPF or DKIM passes and aligns, relying solely on SPF without DKIM introduces vulnerabilities and can subtly impact how mailbox providers perceive your emails. It’s a nuanced area where technical compliance doesn't always equate to optimal inbox placement.
The foundation of reliable email deliverability rests on proper email authentication. SPF, DKIM, and DMARC work in concert to build trust and prevent malicious actors from impersonating your domain. Each plays a distinct yet interconnected role in verifying the legitimacy of your email.
SPF in brief
SPF functions by allowing domain owners to publish a list of authorized sending IP addresses in their DNS records. When an email is received, the recipient's mail server checks the email's return-path domain against the SPF record to confirm that the sending IP is indeed authorized. If the IP isn't on the list, the SPF check may fail, signaling potential spoofing.
DKIM in brief
DKIM provides a cryptographic signature that's attached to the email header. This signature is generated using a private key and can be verified by the receiving server using a public key published in your domain's DNS. A successful DKIM validation confirms that the email (including its headers and body) has not been altered since it was signed by the sending server and that it truly originated from the specified domain.
DMARC's role
DMARC builds upon SPF and DKIM by allowing domain owners to instruct receiving mail servers on how to handle emails that fail authentication and alignment. It also provides reporting capabilities, giving senders visibility into their email authentication performance. DMARC requires that either the SPF or DKIM domain aligns with the From header domain for an email to pass DMARC.
Mechanism
Purpose
Validation Method
Alignment Type
SPF
Authorizes sending IP addresses for a domain
Checks sending IP against authorized list in DNS
Mail From domain (Return-Path)
DKIM
Verifies email content integrity and sender authenticity
Compares cryptographic signature with public key in DNS
d= tag in DKIM-Signature header
DMARC
Policy and reporting for SPF and DKIM authentication
Checks for SPF or DKIM pass and alignment with From header
Header From domain
DMARC's core rule: either or both
DMARC's primary function is to check if an email passes either SPF or DKIM authentication, and if the authenticated domain aligns with the From header domain. If either SPF or DKIM passes and aligns, the DMARC check will pass, regardless of the other's status. This is a crucial point that often leads to confusion.
This mechanism means that if your SPF record is correctly configured and the domain in your email's Return-Path (or Mail From) aligns with your From header domain, your email can technically pass DMARC. Even if DKIM is entirely absent, as long as SPF provides a valid authentication and alignment, DMARC will report a pass. Broadcom's documentation confirms that the absence of a DKIM record will result in DKIM alignment being treated as a fail, but DMARC can still pass if SPF is successful.
However, this technical compliance with DMARC does not mean your email is automatically granted a VIP pass to the inbox. While DMARC is aligned, the absence of DKIM can still raise flags for sophisticated spam filters and major mailbox providers like Google and Microsoft. These systems often consider the presence of both SPF and DKIM as a stronger indicator of legitimacy and a higher quality signal for sender reputation.
This scenario highlights the core of the issue: basic DMARC compliance isn't always synonymous with optimal deliverability. Receiving servers conduct numerous checks beyond DMARC alone, and a missing DKIM signature is a piece of the puzzle that could lead to your emails being viewed with more suspicion. If you encounter DMARC failures, even with seemingly correct SPF, check our guide on troubleshooting DMARC failures and their impact.
The risks of an SPF-only DMARC pass
While a DMARC pass through SPF alone might satisfy the basic authentication requirements, it doesn't mean there are no consequences. The absence of DKIM carries several risks that can negatively affect your email deliverability and overall sender reputation.
Reduced trustworthiness and reputation
Mailbox providers, especially large ones, use a complex set of signals to determine an email's legitimacy. An email with only SPF passing and no DKIM can be seen as a weaker signal of trust. This can lead to lower sender scores and a higher likelihood of your emails landing in the spam folder rather than the inbox.
Spamhaus, an authority on anti-spam efforts, notes that the lack of both SPF and DKIM authentication will damage reputation and affect deliverability. While SPF alone can technically pass DMARC, not having DKIM still signals to receiving servers that your email authentication isn't fully robust. The absence or incorrect implementation of DKIM can have several repercussions, including email delivery challenges, as highlighted by Alore.io's research.
Vulnerability to forwarding issues
SPF can easily break when emails are forwarded, as the sending IP address changes during the forwarding process. If SPF is your only authentication mechanism for DMARC, a forwarded email might fail DMARC completely. DKIM, being tied to the domain via a cryptographic signature, is resilient to forwarding. This makes DKIM crucial for maintaining DMARC pass in such scenarios. For more on this, explore how email forwarding affects SPF, DKIM, and DMARC validation.
Increased spoofing risk
While SPF helps prevent unauthorized IPs from sending on your behalf, it doesn't verify the integrity of the email content itself. DKIM's cryptographic signature ensures that the email content hasn't been tampered with. Without it, your domain is more susceptible to email spoofing and phishing attempts, even if SPF passes, as malicious actors might forge emails that appear to be from your domain, circumventing SPF with compromised IPs or different mail paths.
SPF-only DMARC pass
Potential Deliverability Challenges: Mailbox providers may still apply harsher spam filtering if DKIM is absent, viewing the email as less trustworthy despite DMARC pass.
Vulnerability to Forwarding: SPF can break during email forwarding, leading to DMARC failure and potential rejection, as there's no DKIM fallback.
Increased Spoofing Risk: Lack of a digital signature makes it easier for threat actors to forge emails from your domain without detection by content integrity checks.
SPF + DKIM DMARC pass
Enhanced Deliverability: Mailbox providers view emails with both SPF and DKIM positively, improving inbox placement rates and overall sender reputation.
Resilience to Forwarding: If SPF breaks due to forwarding, DKIM can still ensure DMARC alignment, maintaining authentication and deliverability.
Stronger Anti-Spoofing: The digital signature prevents content tampering and provides strong proof of origin, significantly reducing phishing and spoofing risks.
Strengthening your email authentication posture
Implementing both SPF and DKIM provides a robust defense against email fraud and significantly boosts your email deliverability. This dual authentication approach offers crucial redundancy: if one method encounters an issue, such as SPF breaking due to forwarding, the other can still ensure DMARC alignment and a successful pass.
Best practice dictates that you should strive to pass both SPF and DKIM authentication for all your outbound email streams. This sends a strong, consistent signal of legitimacy to mailbox providers and reduces the likelihood of your emails being flagged as suspicious or ending up in the spam folder. It demonstrates a commitment to email security that recipients and their providers appreciate, leading to better inbox placement.
Regularly monitor your DMARC reports. These reports provide invaluable insights into how your emails are being authenticated by various receivers. By analyzing them, you can identify authentication failures, track alignment issues, and proactively address any weaknesses in your email setup. This is crucial for maintaining a strong sender reputation and ensures you're aware of any potential deliverability impacts. Find out more about understanding and troubleshooting DMARC reports.
Best practice for comprehensive authentication
For optimal deliverability, always aim to have both SPF and DKIM correctly configured and aligned for your sending domains.
DKIM provides a layer of cryptographic assurance that SPF cannot, making your emails more resilient and trusted.
Regularly review your DMARC reports to catch any authentication issues or potential spoofing attempts early.
Views from the trenches
Best practices
Always implement both SPF and DKIM for your sending domains to create a robust authentication framework.
Regularly monitor your DMARC reports to ensure consistent SPF and DKIM pass rates and address any anomalies.
Prioritize DKIM implementation for transactional and critical emails, as it offers a stronger assurance of integrity.
Common pitfalls
Assuming DMARC passing via SPF alone is sufficient for optimal deliverability and strong sender reputation.
Overlooking the impact of email forwarding, which can cause SPF to break and DMARC to fail without DKIM.
Not configuring DKIM at all, leaving the domain more vulnerable to direct domain spoofing and phishing.
Expert tips
Even if DMARC technically passes through SPF alone, mailbox providers often assign higher trust to emails authenticated by both DKIM and SPF.
DKIM's digital signature protects the email's content from tampering, a crucial security feature that SPF doesn't provide.
Forwarding servers frequently break SPF checks. Having DKIM in place ensures DMARC continues to pass even when SPF fails due to forwarding.
Marketer view
Marketer from Email Geeks says that if an email's
May 1, 2023 - Email Geeks
Expert view
Expert from Email Geeks says that DKIM is important to improve email deliverability.
May 1, 2023 - Email Geeks
A holistic approach to email deliverability
Ultimately, while SPF passing and DMARC alignment might lead to a technical DMARC pass, the absence of DKIM is a clear vulnerability in your email authentication strategy. It weakens your overall email security posture, increases the risk of spoofing, and can negatively impact deliverability over time as mailbox providers continue to tighten their authentication requirements. For optimal inbox placement, enhanced security, and a truly robust email program, ensure both SPF and DKIM are properly configured and aligned for all your sending domains.
Google and 
Microsoft. These systems often consider the presence of both SPF and DKIM as a stronger indicator of legitimacy and a higher quality signal for sender reputation.
