How does the absence of DKIM affect email deliverability when SPF is passing and DMARC is aligned?

Key findings

• DMARC compliance: DMARC only requires either SPF or DKIM to pass and align for an email to be considered compliant. If SPF is passing and aligned, the absence of DKIM will not prevent DMARC from passing in most common scenarios.
• Reduced robustness: While not always critical for DMARC passing, omitting DKIM can make your email authentication less robust. DKIM provides an additional layer of verification that protects email content from tampering.
• Forwarding issues: SPF can break when emails are forwarded, as the forwarding server's IP address might not be authorized by the original SPF record. In such cases, a valid DKIM signature can maintain DMARC compliance, preventing the email from being rejected or sent to spam.
• Sender reputation: Having both SPF and DKIM properly implemented and aligned significantly strengthens your domain's sender reputation with mailbox providers. This dual authentication signals legitimacy and helps improve inbox placement over time.
• Stricter recipient policies: Some mailbox providers or individual recipient configurations may have stricter policies that prefer or even require both SPF and DKIM to pass. While not universally enforced, this can impact deliverability to specific recipients.

Key considerations

• Implement DKIM: Even if SPF is passing, it is highly recommended to implement DKIM for added security and deliverability benefits. This provides redundancy and a more robust authentication posture, as detailed in our guide on DMARC, SPF, and DKIM.
• Monitor DMARC reports: Regularly review your DMARC reports to understand how your emails are authenticating across different receivers. This can help identify any unexpected failures or areas for improvement, even if DMARC is currently passing. Learn more about common DMARC pitfalls.
• Consider email forwarding: If your recipients frequently forward emails, DKIM's resilience to forwarding changes becomes critical for maintaining DMARC compliance. Understanding how email forwarding affects DMARC is important.
• Align both protocols: Aim to have both SPF and DKIM properly configured and aligned with your organizational domain. This dual alignment provides the best possible protection against spoofing and maximizes deliverability.

Key opinions

• Basic DMARC passing: Many marketers understand that DMARC can pass if either SPF or DKIM aligns, so if SPF is correctly set up, a missing DKIM might not immediately trigger a DMARC failure.
• Impact on deliverability: There's a general consensus that DKIM is crucial for overall deliverability improvement, even if DMARC passes via SPF. It adds another layer of trust.
• Authentication visibility: Marketers frequently check email headers (like in Gmail's 'Show original') to verify authentication status, and the absence of a DKIM signature is a noticeable gap.
• Reputation building: A full suite of authentication (SPF, DKIM, DMARC) is seen as essential for building a strong sender reputation and avoiding filters, blocklists, and getting flagged as spam.
• Proactive measures: While immediate issues might not arise, marketers often prefer to proactively address any missing authentication elements to future-proof their email programs.

Key considerations

• Complete authentication: Even if DMARC passes with SPF alone, implement DKIM for a complete authentication strategy that enhances overall deliverability and resilience, particularly against email forwarding challenges.
• Domain reputation: Recognize that a strong domain reputation is built on consistent and comprehensive authentication. Missing DKIM, even if not immediately failing DMARC, can subtly impact how mailbox providers view your sending domain. Our guide on recovering domain reputation highlights the importance of consistent practices.
• Monitoring and troubleshooting: Regularly check email headers and DMARC reports for any authentication discrepancies. Being proactive in identifying and fixing issues can prevent deliverability problems down the line, as discussed in our article on troubleshooting DMARC failures.
• Meeting receiver expectations: Understand that while DMARC provides a baseline, some receiving servers may have stricter internal policies or algorithms that favor domains with both SPF and DKIM properly set up. Duocircle provides a helpful guide on how DKIM alignment affects DMARC.

Key opinions

• DMARC flexibility: Experts confirm that DMARC is designed to pass if either SPF or DKIM is aligned, so if SPF is passing and aligned, DKIM's absence might not cause DMARC failure.
• Forwarding resilience: DKIM is vital for maintaining DMARC compliance through email forwarding, where SPF often breaks due to changes in the sending path.
• Strengthening reputation: A complete authentication setup with both SPF and DKIM significantly enhances sender reputation and reduces the likelihood of emails being flagged as suspicious or blocked.
• Proactive security: Relying on SPF alone makes a domain more vulnerable to spoofing if that SPF record is compromised, whereas DKIM provides an additional layer of cryptographic verification.
• Long-term deliverability: While immediate issues may not appear, the absence of DKIM can negatively affect long-term deliverability and inbox placement as receiving systems evolve their filtering criteria.

Key considerations

• Comprehensive authentication: Always aim to implement both SPF and DKIM, even if DMARC technically passes with just one. This dual approach provides maximum protection and deliverability benefits, as detailed in our comprehensive guide to boosting email deliverability rates.
• DMARC policy hardening: Once both SPF and DKIM are robustly implemented, consider transitioning your DMARC policy from p=none to p=quarantine or p=reject to enforce stronger anti-spoofing measures. Learn how to safely transition your DMARC policy.
• Recipient server behavior: Be aware that some email servers (like Customer.io has indicated for their sending) may require both SPF and DKIM to be verified for email to be sent from a domain, even if DMARC technically allows one to pass. This underscores the value of dual authentication.
• Consistent monitoring: Utilize tools and services to continuously monitor your DMARC reports, providing insights into potential authentication failures or areas where DKIM could strengthen your email program. MessageFlow provides a good explanation of SPF, DKIM, and DMARC protocols.

Key findings

• DMARC mechanism: DMARC is designed to pass if either the SPF check passes with alignment or the DKIM check passes with alignment. If SPF is passing and aligned, DKIM is not strictly required for DMARC to authenticate the email.
• SPF limitations: SPF validates the sender's IP address against a list of authorized IPs for the domain. Its vulnerability lies in scenarios like email forwarding, where the IP address changes, potentially causing SPF to break.
• DKIM's role: DKIM provides a cryptographic signature that validates the email's integrity and sender's domain, remaining intact even through forwarding, thus providing resilience where SPF fails.
• Enhanced authentication: Official best practices and security guidelines consistently recommend implementing both SPF and DKIM for comprehensive email authentication, as they complement each other to create a stronger defense against spoofing and phishing.

Key considerations

• RFC compliance: Adhere to the RFCs for SPF, DKIM, and DMARC to ensure proper configuration and optimal performance. While DMARC allows flexibility, full implementation provides maximum benefits.
• Robust security: Implement DKIM even if SPF is passing, as it adds a critical layer of security by verifying message integrity, making your domain more secure against various forms of email abuse.
• Future-proofing: Stay updated with evolving email authentication best practices and receiving server requirements. While currently SPF might suffice, future policy changes could emphasize dual authentication. Our guide on the benefits of implementing DMARC outlines these advantages.
• Reporting analysis: Leverage DMARC aggregate reports to gain visibility into your email authentication status. These reports can show if SPF or DKIM is passing for different receivers, helping you identify areas for improvement. Understanding DMARC reports from Google and Yahoo is key.