Why is my DMARC failing even though DKIM and SPF pass in Sendgrid?

Key findings

• DMARC alignment: DMARC requires that either the SPF Return-Path domain or the DKIM d= (signing) domain aligns with the email's From: header (RFC5322.From) for DMARC to pass. A common DMARC failure reason is misalignment, even if SPF and DKIM pass their individual checks.
• Third-party senders: When using a service like SendGrid, the default SPF and DKIM domains often belong to the sending service (e.g., sendgrid.net). For DMARC alignment, you need to configure domain authentication within SendGrid and publish the corresponding DNS records (CNAMEs) on your own domain.
• DKIM signature: While a DKIM signature might be present and verified, if the d= tag in the DKIM signature is not your actual sending domain (or a subdomain), DMARC will fail alignment for DKIM.
• SPF alignment: Similarly, if the Return-Path domain (also known as Mail From or Envelope From) does not align with your From: header, DMARC SPF alignment will fail.
• DMARC policy: A p=reject DMARC policy instructs receiving mail servers to block emails that fail authentication and alignment. This makes troubleshooting critical. For more on DMARC policies, read our guide to DMARC tags and their meanings.

Key considerations

• Check headers: Obtaining and inspecting the full email headers is crucial to diagnose DMARC failures. Look specifically at the Authentication-Results header for SPF, DKIM, and DMARC results, paying close attention to the domains involved in each check (e.g., smtp.mailfrom, header.d, and header.from). This can reveal why DMARC authentication fails.
• Domain authentication in SendGrid: Ensure your domain is fully authenticated within SendGrid, not just added. This involves setting up CNAME records for DKIM and a TXT record for SPF. Crucially, verify that these authenticated domains are correctly associated with the specific subusers or sending accounts within SendGrid that are sending the emails. SendGrid provides documentation on addressing email delivery failures from DMARC.
• API configuration: If you're sending via API, double-check that your API calls are correctly referencing the authenticated domain or the correct subuser that has the domain assigned. A misconfiguration here can lead to SendGrid using its default domains for authentication instead of yours.
• DMARC reports: Regularly review your DMARC aggregate (RUA) reports. These reports provide valuable insights into which emails are failing DMARC, why they are failing (e.g., SPF or DKIM misalignment), and where they are being sent. Monitoring these reports helps to troubleshoot DMARC failures.

Key opinions

• Initial confusion: Marketers are often puzzled when their DMARC reports show failures despite SPF and DKIM appearing to pass in their sending platform's dashboard. They might verify DNS settings and still see blocks.
• Headers are key: The consensus is to always examine the raw email headers from a failing email. This provides the definitive authentication results, showing precisely which domains passed authentication and which failed DMARC alignment (e.g., header.d=sendgrid.net;dmarc=fail).
• Alignment over authentication: A common misunderstanding is that passing SPF and DKIM authentication is enough for DMARC. Marketers discover that DMARC explicitly requires alignment between the authenticated domains and the From: header.
• Subuser assignments: A specific challenge with platforms like SendGrid is the need to explicitly assign authenticated domains to subusers, even if the domain is authenticated at the root level. This can be a subtle but critical step often missed due to unclear documentation.

Key considerations

• Verify full configuration: Don't just rely on a platform's UI saying 'validated.' Marketers need to ensure that the entire setup, including domain assignment to specific sending entities (like subusers), is complete and active. This will help prevent issues where emails go to spam due to DMARC alignment.
• Leverage testing tools: When troubleshooting, marketers should use email testing tools or send to email providers that don't reject DMARC failures outright (like Microsoft Outlook/Hotmail, which often move them to junk), allowing for header inspection.
• Understand domain branding: For proper DMARC alignment, marketers must ensure that their sending platform (e.g., SendGrid) is configured to use their own domain for both the SPF Return-Path and DKIM d= (signing) domains, aligning with the From: header. This is often achieved through custom domain setup or whitelabeling.
• Engage support: If issues persist after thorough checks, marketers should escalate the problem to their email service provider's support team, providing full email headers and outlining their troubleshooting steps.

Key opinions

• Alignment is crucial: Experts agree that the root cause of DMARC failure, even when SPF and DKIM pass, is a lack of alignment between the authenticated domains and the From: header. This is a common DMARC verification failed error.
• DKIM domain mismatch: If the DKIM signature is valid but signed by an unrelated domain (e.g., sendgrid.net instead of yourdomain.com), DMARC will fail DKIM alignment.
• SPF domain mismatch: Similarly, if the SPF Return-Path domain doesn't align with the From: header, DMARC will fail SPF alignment.
• Platform-specific settings: Many DMARC failures with ESPs like SendGrid are due to internal platform settings not fully activating the client's domain for authentication, even if DNS records are correctly published. The ESP may need to turn something on or there might be an overlooked assignment (e.g., to a subuser).

Key considerations

• Full header analysis: Always obtain the full email headers to pinpoint the exact reason for DMARC failure. This allows you to see the domains associated with spf, dkim, and dmarc authentication results side-by-side with the From: domain. For deeper insights, you can review our guide on troubleshooting DMARC reports.
• Domain branding in ESPs: To achieve DMARC alignment, ensure your ESP (like SendGrid) is configured for whitelabeling or custom domain setup, which modifies the Return-Path and DKIM d= domains to use your own domain or a subdomain thereof.
• Test with different mailboxes: Sending test emails to various mailbox providers (e.g., Outlook.com, Gmail) is helpful. Some, like Microsoft, may not immediately reject DMARC failures but instead deliver to the junk folder, providing an opportunity to examine the headers for the 'reason=000' status.
• Consult ESP support: If all DNS records and internal configurations appear correct, and alignment is still failing, it's appropriate to engage your ESP's support. There might be a backend setting or an undocumented requirement within their system causing the issue.

Key findings

• DMARC requirement: DMARC requires that the domain used for SPF (Mail From) or DKIM (d=tag) authentication aligns with the RFC5322.From header domain. If this alignment does not occur, DMARC will fail.
• SendGrid domain authentication: SendGrid's documentation (Twilio SendGrid) explains that users must set up 'domain authentication' (often referred to as whitelabeling) to ensure that emails are sent from their domain and align with DMARC. This involves publishing specific CNAME records for DKIM and potentially updating SPF records.
• Strict DMARC policies: If a DMARC policy is set to 'p=reject', any email failing DMARC alignment will be blocked by the receiving mail server. This makes proper configuration crucial.
• Subdomain usage: For SPF alignment, some providers may recommend adding their IP directly to your SPF record or using a specific subdomain for the Return-Path. For DKIM, the 'd=' tag needs to match your 'From:' domain or a close subdomain to achieve alignment.

Key considerations

• CNAME records for DKIM: For SendGrid, typically two CNAME records are provided for DKIM setup that point back to SendGrid's infrastructure. These must be correctly published in your DNS for DKIM to authenticate and align properly with your domain.
• Dedicated IP and SPF: If using a dedicated IP with SendGrid, documentation suggests adding the dedicated IP directly to your domain's SPF record to correct SPF alignment issues. This method ensures your domain explicitly authorizes the SendGrid IP.
• Review ESP-specific guides: Always refer to the specific email service provider's documentation (e.g., SendGrid's support articles) for detailed instructions on domain authentication and DMARC alignment troubleshooting. Their guides often contain platform-specific nuances that can resolve complex issues. For example, SendGrid's troubleshooting guide for DMARC policy failures is a valuable resource.
• DMARC reports for diagnosis: Documentation often recommends analyzing DMARC aggregate (RUA) reports. These XML reports detail authentication results, including alignment status (strict or relaxed), which helps in identifying why DMARC is failing.