SPF flattening involves converting complex SPF records with multiple mechanisms (like 'include', 'a', 'mx') into a simplified record containing only IP addresses. This is primarily done to overcome the 10 DNS lookup limit, which is a common cause of SPF PermErrors that can impact email deliverability. However, implementing SPF flattening can introduce complexities when using email evaluation tools like MxToolbox or Litmus, as these tools may struggle to correctly interpret flattened records or SPF macros.
Key findings
Tool limitations: Many email evaluation tools, including common ones like MxToolbox and Litmus, often struggle to accurately evaluate SPF records that have been flattened or contain SPF macros. This can lead to false positives where the tool reports an error, even if the record is functionally correct.
Dynamic vs. static: SPF flattening transforms dynamic SPF records (which pull in includes from other services) into static lists of IP addresses. While this helps with the 10 DNS lookup limit, it means the record needs manual updates whenever a sending IP changes.
Reliability concerns: Relying solely on flattened SPF records (especially those with only IP addresses) may not be the most reliable solution for long-term email authentication, as the underlying IPs of third-party sending services can change.
Deliverability enhancement: Despite evaluation tool challenges, SPF flattening primarily aims to reduce DNS lookups, which directly enhances email deliverability by preventing SPF failures.
Key considerations
Tool discrepancies: Be aware that different email deliverability testing tools may provide varying results when checking SPF records, particularly when flattening or macros are involved. It is advisable to use multiple checkers or an SPF checker designed to handle macros correctly, such as Kitterman's SPF Record Checker.
Dynamic updates: If using SPF flattening, implement a system for regular monitoring and updating of your SPF record. This ensures that any changes to sending IPs from your email service providers are quickly reflected, preventing SPF failures.
Comprehensive authentication: While SPF is foundational, ensure you also implement DKIM and DMARC for robust email authentication. DMARC provides reporting that can help identify SPF failures and guide policy adjustments.
Alternatives to flattening: Consider if SPF flattening is truly necessary. Sometimes, simply optimizing your SPF record by removing redundant or unnecessary mechanisms can bring it under the 10 DNS lookup limit without requiring flattening.
Email marketers frequently encounter challenges with SPF records, particularly when attempting to manage complex sending infrastructures or comply with the 10 DNS lookup limit. Many turn to SPF flattening services or SPF macros as solutions, only to find that common email evaluation tools report issues, leading to confusion and friction with their IT teams.
Key opinions
Tool inaccuracies: Marketers often report that tools like MxToolbox and Litmus sometimes show incorrect SPF errors, especially when SPF flattening or macros are used, even if their IT team confirms the record is valid.
Seeking validation: There's a strong desire among marketers for reliable SPF validation tools that can accurately interpret complex SPF setups without providing misleading error messages.
Practical solutions: Marketers look for practical advice on how to correctly configure SPF to avoid deliverability issues, whether through flattening or other methods.
Impact on campaigns: SPF issues, regardless of their origin, are a major concern for marketers because they can directly lead to emails landing in spam folders, reducing campaign effectiveness and ROI.
Key considerations
Verify with multiple tools: If one tool reports an SPF error, especially with a flattened record, cross-reference it with other reliable SPF checkers to confirm the issue. This helps distinguish between actual configuration problems and tool limitations.
Understand underlying causes: Work with your IT team to understand why your SPF record might be flagged as 'too long' or complex. This helps in determining if flattening is truly the best approach or if simpler optimizations are possible.
Monitor deliverability directly: While evaluation tools are useful, the ultimate test is actual inbox placement. Use deliverability monitoring platforms to track your emails' journey to the inbox, which provides real-world feedback on your SPF configuration.
Educate internal teams: Ensure both marketing and IT teams understand the nuances of SPF, including flattening and macros, and their implications for deliverability and tool interpretation. This helps align expectations and troubleshooting efforts. You may want to brush up on this topic with Mailgun's guide to email authentication.
Marketer view
Marketer from Email Geeks indicates that they are encountering an issue where Litmus and MxToolbox are reporting problems with their SPF record, despite their IT team confirming that the setup is correct. They are questioning if SPF flattening could be the cause of this discrepancy.
22 Sep 2024 - Email Geeks
Marketer view
Marketer from SendLayer Blog notes that SPF flattening simplifies SPF records by directly listing IP addresses, which can make it easier to visually inspect which senders are authorized for a domain. This is useful for quick verification.
24 Jul 2024 - SendLayer Blog
What the experts say
Experts in email deliverability acknowledge that SPF flattening and the use of SPF macros are valid strategies for managing complex SPF records and staying within the 10 DNS lookup limit. However, they also confirm that many existing SPF evaluation tools are not designed to accurately process these advanced configurations, leading to widespread confusion among users and misinterpretations of SPF record health.
Key opinions
Tool limitations confirmed: Many SPF checkers, including widely used ones, indeed have difficulty correctly interpreting SPF macros and flattened records, often leading to false error reports.
Need for advanced checkers: There's a recognized need for more sophisticated SPF validation tools that can accurately parse and evaluate records employing macros and flattening techniques.
Optimizing SPF first: Some experts suggest questioning the necessity of flattening if the record contains many unnecessary elements. Streamlining the record might be a better first step.
Real-world testing: Testing SPF records by sending emails to major mailbox providers (like Gmail) and inspecting the headers is often considered more reliable than relying solely on automated checkers.
Key considerations
Prioritize proper record structure: Before resorting to flattening, ensure your SPF record only includes essential 'include' mechanisms and 'ip4' or 'ip6' addresses. This can often resolve DNS lookup issues without flattening.
Utilize specialized tools: When SPF flattening or macros are in use, use SPF checkers known to handle these features correctly. Some resources also provide best practices for using SPF flatteners.
Monitor real-time impact: Rely on DMARC reports for accurate insights into how mailbox providers are evaluating your SPF, DKIM, and DMARC records in practice. This offers a true picture of authentication success rates. Consider SpamResource for expert insights on these topics.
Stay updated: The landscape of email authentication and evaluation tools evolves. Staying informed about updates and new features in SPF checkers and DMARC reporting tools is crucial for accurate troubleshooting. This is especially true for understanding when SPF flattening is necessary for email authentication.
Expert view
Expert from Email Geeks (Steve589) clarifies that many SPF evaluation tools indeed have trouble correctly processing SPF macros. This suggests that the issues reported by tools like MxToolbox and Litmus could stem from this incompatibility.
09 Oct 2024 - Email Geeks
Expert view
Expert from Word to the Wise (Steve589) admits that their own SPF checker at tools.wordtothewise.com "fails horribly" on SPF macros. This highlights the widespread nature of the issue across various evaluation platforms.
09 Oct 2024 - Word to the Wise
What the documentation says
Official documentation and technical guides confirm that SPF flattening is a workaround for the 10 DNS lookup limit inherent in SPF. While it addresses this specific technical constraint, the process of flattening itself can introduce complexities that may not be fully supported by all SPF evaluation tools, which are often built to parse the original SPF record syntax.
Key findings
DNS lookup limit: SPF specifies a maximum of 10 DNS lookups during validation. Exceeding this limit results in a 'PermError', which can lead to emails being rejected or marked as spam.
Flattening mechanism: Flattening typically involves resolving all 'include', 'a', and 'mx' mechanisms in an SPF record to their underlying IP addresses and listing them directly in the TXT record, thus avoiding additional DNS lookups during validation.
Tool interpretation: Evaluation tools vary in their ability to correctly interpret flattened SPF records or those using advanced features like SPF macros. Some may simply report the flattened record as incomplete or erroneous because they expect the original, dynamic syntax.
Maintenance implications: Flattened records require manual or automated updates whenever the IP addresses of the included services change, unlike dynamic records that automatically reflect changes.
Key considerations
Dynamic vs. static management: Organizations must weigh the benefits of avoiding DNS lookup errors with the increased management overhead of maintaining a static, flattened SPF record, as detailed in guides on choosing the right SPF approach.
Service provider changes: Changes to sending infrastructure or email service providers (ESPs) that are 'included' in your SPF record necessitate an update to your flattened record to prevent authentication failures.
SPF macro usage: While macros offer a dynamic alternative, their complexity means fewer tools (and sometimes fewer mailbox providers) fully support their parsing, potentially leading to similar evaluation issues as flattening, as outlined in URIports' discussion on SPF macros.
Holistic authentication: Documentation consistently emphasizes that SPF should be part of a broader email authentication strategy that includes DKIM and DMARC for comprehensive spoofing protection and deliverability. This ensures that even if SPF has complexities, other authentication methods can still pass.
Technical article
Documentation from AutoSPF Blog explains that SPF flattening reduces the number of records that require updating, offering a simpler management approach compared to frequently changing multiple 'include' mechanisms.
01 Mar 2024 - AutoSPF Blog
Technical article
Documentation from URIports Blog discusses how flattening an SPF record to include only ip4 and ip6 addresses can decrease DNS lookups, but cautions that it may not always be the most reliable long-term solution due to its static nature.