Do I need to include Mailchimp's SPF record in my domain's SPF if Mailchimp handles the bounce address?

Key findings

• SPF authentication: SPF checks the Return-Path (envelope from) address, not the "From" address visible to recipients. If Mailchimp uses its own domain for the Return-Path, your domain's SPF record is not directly evaluated for SPF authentication of those emails.
• DNS lookup limit: SPF records have a strict 10-DNS lookup limit. Including unnecessary includes, such as one for an ESP that uses its own bounce domain, can cause your SPF record to exceed this limit, leading to an SPF PermError for recipient servers that strictly enforce the RFC. This can negatively impact your email deliverability, even if some receivers might still pass the SPF check.
• DMARC alignment: Even if SPF passes on Mailchimp's domain, it will not align with your "From" domain for DMARC. Therefore, DKIM becomes the primary authentication method for DMARC alignment when sending through ESPs like Mailchimp that use their own bounce domain. Ensure your DKIM setup is robust for your domain.
• ESP-specific configurations: Mailchimp's current documentation generally emphasizes DKIM authentication (via CNAME records) for sender domain authentication, implying that including their SPF record is not typically required when they handle the bounce address. This is a crucial detail for proper authentication setup.

Key considerations

• Verify Return-Path: Always inspect the email headers to determine the actual Return-Path domain used by your ESP. If it's not your domain (e.g., Mailchimp's domain), then your domain's SPF record is not directly responsible for that email's SPF authentication.
• Prioritize DKIM: Given that ESPs often handle the SPF check on their own bounce domain, ensure your DKIM authentication for your "From" domain is correctly set up. This is usually sufficient for DMARC alignment and critical for building your sender reputation. For more on this, refer to our guide on the impact of the 'From' domain record on SPF.
• Monitor DMARC reports: DMARC reports provide invaluable insights into how your SPF and DKIM are performing and whether they are aligning with your "From" domain. Pay close attention to these reports to understand your authentication status. You can learn more about this in our article on DMARC.
• Simplify SPF records: Aim to keep your SPF record concise and below the 10-lookup limit. If an ESP is handling the bounce address on their own domain, remove their include from your SPF record to prevent potential PermErrors and simplify your DNS management. Our guide Why you shouldn't add MailChimp to your SPF record covers this in detail.
• Utilize subdomains: For different sending purposes (e.g., transactional vs. marketing), consider using subdomains with their own SPF records. This can help manage lookup limits and isolate sending reputation.

Key opinions

• Misconceptions about SPF: Many marketers are confused about the purpose of SPF, incorrectly assuming it authenticates the From domain rather than the Return-Path (bounce address).
• Outdated advice: There are still articles and resources online that recommend including ESPs like Mailchimp in your domain's SPF, even if the ESP handles the bounce address on their own domain. Marketers often follow this advice, unaware it might be outdated or incorrect for their specific setup.
• Observed inconsistencies: Marketers sometimes report conflicting SPF pass/fail results from different testing tools or Postmaster services (like Google Postmaster Tools), even when email headers show consistent SPF passes for the ESP's bounce domain.
• Focus on DMARC and DKIM: Many marketers prioritize DKIM setup with their ESPs because it's often the recommended method for aligning with their "From" domain for DMARC, especially when the ESP uses its own SPF. This aligns with modern email authentication best practices.

Key considerations

• Trust ESP documentation: Rely primarily on your ESP's official documentation for authentication setup, as it reflects their current sending infrastructure and best practices. Mailchimp's current guidance, for instance, focuses on DKIM for custom domain authentication.
• Educate clients: Be prepared to explain the nuances of SPF, DKIM, and DMARC to clients, especially when changes to DNS records might lead to unexpected reporting in tools like Google Postmaster Tools. Emphasize that DKIM is usually the primary alignment mechanism for DMARC when using a third-party ESP.
• Avoid SPF lookup limits: Actively manage your SPF record to stay within the 10-DNS lookup limit. Removing unnecessary includes, especially for ESPs that handle their own bounce domain, is a critical step in maintaining a valid SPF record. Overly complex SPF records can lead to SPF PermErrors, impacting your email deliverability.
• Leverage DMARC reporting: Utilize DMARC reports to identify authentication failures. While SPF might fail DMARC alignment if your ESP uses their own Return-Path, a passing DKIM authentication will typically ensure DMARC passes for your domain. This provides a clearer picture than relying solely on individual SPF checks in isolated tests, as detailed in this Mailchimp article on email authentication.

Key opinions

• SPF scope: SPF is solely about authenticating the bounce address. You typically do not need to add every ESP you use to the SPF record of your primary corporate domain if the ESP sets the bounce address on their own domain.
• RFC compliance and limits: While the SPF specification dictates a 10-DNS lookup limit, some receivers are more lenient or have higher internal limits. However, strictly compliant receivers will fail SPF if this limit is exceeded, leading to a PermError.
• DMARC reliance on DKIM: If SPF authenticates the ESP's domain (because they control the Return-Path), it will not achieve DMARC alignment with your "From" domain. In such cases, DKIM authentication (signing with your domain) becomes critical for DMARC to pass and for your email to be authenticated successfully.
• Misleading testing tools: Experts express confusion when tools like Google Postmaster Tools show a 100% SPF pass rate for a sender's domain even when the SPF record in question is for the ESP's bounce domain. This suggests potential misinterpretation or non-standard reporting by such tools.

Key considerations

• Custom Return-Paths/subdomains: For better control over SPF and to avoid lookup limits on your main domain, consider using custom return paths or subdomains for different ESPs. This allows you to set SPF records specific to those subdomains, improving overall authentication posture. Refer to our guide on best practices for DNS lookups.
• Focus on DMARC deployment: If you are deploying DMARC, ensure your DKIM setup is robust for your "From" domain. Since SPF often won't align when using an ESP's bounce domain, DKIM becomes the primary mechanism for DMARC authentication. Our page on a simple guide to DMARC, SPF, and DKIM can provide more context.
• Inspect headers and DMARC reports: Always inspect the raw email headers and analyze DMARC reports to get the most accurate picture of how your SPF and DKIM are being evaluated by recipient servers. These provide more reliable data than some aggregated Postmaster Tools statistics, especially when attempting to debug SPF compliance issues with Google Postmaster Tools.
• Avoid unnecessary includes: Remove any ESP SPF includes from your main domain's SPF record if the ESP handles bounce addresses on its own domain. This cleans up your SPF, reduces lookup counts, and prevents potential PermErrors, ultimately improving your overall email deliverability rates.

Key findings

• SPF validation point: SPF validates the domain found in the SMTP "MAIL FROM" command, also known as the Return-Path or bounce address. This is distinct from the "From" header (RFC5322.From) that users typically see. Mailchimp's documentation implies their system handles this aspect of SPF on their own behalf.
• Mailchimp's authentication approach: Mailchimp's current documentation primarily focuses on enabling DKIM authentication for custom domains. They typically provide CNAME records for DKIM setup, which allows emails to be signed with the sender's domain, facilitating DMARC alignment.
• DMARC mechanism: DMARC relies on either SPF or DKIM to pass authentication. Crucially, it also requires that the domain verified by SPF (the Return-Path domain) or DKIM (the d= domain) aligns with the domain in the "From" header. If Mailchimp sets the Return-Path to their domain, SPF will pass for their domain, but it won't align with your From domain for DMARC.
• Implicit SPF handling: Mailchimp (and many other ESPs) automatically handle SPF authentication for their sending infrastructure. This means they ensure their own sending IPs are authorized within their own SPF records, which are then checked against their Return-Path domain.

Key considerations

• Understand SPF's role: Recognize that SPF authenticates the Return-Path, not the From address directly. If an ESP uses its own Return-Path, your SPF record isn't relevant for that SPF check. For a deeper dive, review the basics of RFC 5322 and its practical implications.
• Prioritize DKIM for DMARC alignment: To achieve DMARC compliance and build domain reputation, ensure your DKIM is properly configured with your ESP. This is usually sufficient for aligning your "From" domain with an authenticated entity, even if SPF doesn't align.
• Refer to current ESP guides: Always consult the most up-to-date authentication guides provided by your ESP. For instance, Mailchimp's current help articles, like "About Email Domain Authentication" and "How to Set Up Email Domain Authentication," offer the most accurate guidance on their recommended setup for SPF, DKIM, and DMARC.
• Avoid redundancy: If an ESP confirms they handle the bounce address on their own domain, refrain from including their SPF mechanism in your primary domain's SPF record. This prevents exceeding the 10-lookup limit and avoids unnecessary complexity, which can cause SPF PermErrors as discussed in "Why your emails fail at Microsoft: the hidden SPF DNS timeout" (a good resource, though specific to Microsoft).