What are the options for dealing with overstuffed SPF records exceeding DNS lookup limits?

Summary

Dealing with overstuffed SPF records exceeding the 10 DNS lookup limit requires a multi-faceted approach. Documentation highlights the importance of the limit and potential deliverability issues. Experts and marketers suggest options such as simplifying SPF records by removing unnecessary includes, relying on DKIM (and DMARC) as alternative authentication methods, employing SPF flattening (with careful maintenance), utilizing subdomains or dedicated sending domains, and regularly auditing/optimizing SPF records. Hosted SPF services and external authentication services can also resolve the lookup limit. The key is to ensure that the chosen methods are implemented correctly and maintained to achieve optimal email deliverability and authentication.

Key findings

  • 10 Lookup Limit: SPF records are limited to 10 DNS lookups.
  • DKIM/DMARC Reliance: DKIM and DMARC provide alternative authentication and should be used alongside SPF.
  • SPF Flattening: SPF flattening reduces lookups but requires continuous IP monitoring.
  • Sub/Dedicated Domains: Using subdomains or dedicated sending domains simplifies SPF management.
  • Regular Audits: Regularly auditing and removing obsolete entries keeps SPF records lean.
  • Hosted SPF: Hosted SPF services bypass the lookup limit.
  • Record Optimization: Regular review and optimization of SPF records are crucial.
  • Tools and Checkups: Tools exist to identify includes that contribute to the DNS lookup limit.

Key considerations

  • Maintenance: SPF flattening requires ongoing maintenance to update IP addresses.
  • ISP Forgiveness: Relying on ISP leniency is not a reliable long-term solution.
  • Correct Setup: Ensure correct SPF, DKIM, and DMARC setup for optimal email deliverability.
  • Potential Bad Guidance: Be cautious of potentially poor advice from ESPs regarding SPF configuration.
  • Ongoing Effort: Managing SPF records requires continuous monitoring and optimization.
  • External Cost: Implementing and maintaining external services requires money.

What email marketers say
13Marketer opinions

When SPF records exceed the 10 DNS lookup limit, several options exist. These include relying solely on DKIM, employing SPF flattening (though this requires ongoing maintenance), using subdomains for different email streams, migrating to dedicated sending domains, regularly auditing and removing obsolete entries, and using external services to manage SPF and DKIM. Hosted SPF services, like those offered by Proofpoint, can also resolve lookup limits. It's generally advised to use SPF in conjunction with DKIM and DMARC for robust email authentication.

Key opinions

  • DKIM Reliance: DKIM can serve as a robust alternative to SPF when SPF records are too complex.
  • SPF Flattening: SPF flattening reduces lookups but requires constant IP address monitoring.
  • Subdomain Usage: Using subdomains for different email types simplifies SPF records.
  • Dedicated Domains: A dedicated sending domain allows for a more streamlined SPF record.
  • Record Auditing: Regularly auditing and removing old entries keeps SPF records lean.
  • Hosted SPF: Hosted SPF services bypass the lookup limit.
  • External Services: External services can manage SPF and DKIM complexities.
  • Importance of Checkup Tools: By checking the SPF record, you can identify which includes are causing additional lookups, and see if any can be removed or consolidated.

Key considerations

  • Maintenance: SPF flattening requires ongoing monitoring and updates.
  • Complexity: Consider the complexity of implementing and managing different solutions.
  • Authentication Standards: Ensure proper SPF, DKIM, and DMARC implementation for best results.
  • Service Costs: External services may incur additional costs.
  • Business Migration: The business may need to think about a full domain migration
Marketer view

Email marketer from StackOverflow mentions using a dedicated sending domain or subdomain for email marketing. This allows for a simpler SPF record that only includes the necessary services for that specific sending domain, reducing the risk of exceeding the lookup limit.

September 2023 - StackOverflow
Marketer view

Email marketer from Reddit suggests migrating entirely to DKIM. If SPF is too difficult to manage, DKIM offers a robust alternative for authentication without the DNS lookup limitations of SPF. It involves digitally signing emails, which is verified by the receiving server.

October 2023 - Reddit
Marketer view

Email marketer from AuthSMTP says to use external authentication services for SPF and DKIM. These services can handle the complexity of SPF records and ensure compliance with DNS lookup limits, providing a managed solution for email authentication.

May 2023 - AuthSMTP
Marketer view

Marketer from Email Geeks (Proofpoint) states that Proofpoint has something called Hosted SPF that resolves the 10 DNS lookup limit.

July 2023 - Email Geeks
Marketer view

Email marketer from DNSQueries highlights the option of using services that automatically flatten your SPF records. These services monitor your includes and automatically update the SPF record with the resolved IP addresses, ensuring you stay within the lookup limit without manual intervention.

April 2022 - DNSQueries
Marketer view

Marketer from Email Geeks suggests that many clients rely on DKIM only because of SPF record issues, and offers flattening as another option, mentioning providers and self-hosted options.

June 2024 - Email Geeks
Marketer view

Email marketer from EmailonAcid shares that you can review your SPF record regularly and remove any outdated or unnecessary entries, and only include the sending sources that are currently in use. This helps maintain a lean SPF record and avoid exceeding the lookup limit.

April 2022 - EmailonAcid
Marketer view

Email marketer from Gmass shares that regularly auditing your SPF records and removing old services or providers that are no longer in use, helps in reducing the number of lookups, and is a practical method to stay within the limit.

March 2025 - Gmass
Marketer view

Marketer from Email Geeks warns that flattening is a nightmare if anyone changes their SPF that you might have in an include for. Suggests a method of splitting up spf records.

June 2022 - Email Geeks
Marketer view

Email marketer from MXToolbox answers that they provide tools to check the SPF record, and by checking the SPF record, you can identify which includes are causing additional lookups, and see if any can be removed or consolidated.

June 2024 - MXToolbox
Marketer view

Email marketer from SendGrid states that while SPF is useful, DKIM and DMARC are important for authentication. If SPF is complex, focus on DKIM signing and DMARC policy to ensure emails are properly authenticated even if SPF fails due to lookup limits.

December 2022 - SendGrid
Marketer view

Email marketer from EasyDMARC explains that SPF flattening is a technique to reduce the number of DNS lookups in an SPF record by replacing 'include' statements with the actual IP addresses they resolve to. This can help avoid exceeding the 10-lookup limit but requires regular maintenance to update IP addresses when they change.

February 2025 - EasyDMARC
Marketer view

Email marketer from Mailjet shares that using subdomains for different sending purposes, like transactional emails versus marketing campaigns, allows you to create separate SPF records with fewer includes for each. This prevents SPF records from becoming too complex and exceeding the lookup limit.

May 2023 - Mailjet

What the experts say
4Expert opinions

Experts suggest several approaches to handling overstuffed SPF records exceeding DNS lookup limits. These include reviewing and optimizing existing records by removing obsolete entries and consolidating includes, using dedicated domains for the 5321.from, and taking the opportunity to create a streamlined SPF record when migrating to a new ESP. Ignoring the issue, though some ISPs are forgiving, is not recommended.

Key opinions

  • Record Optimization: Regular review and optimization of SPF records are crucial.
  • Dedicated Domains: Using dedicated domains for sending can simplify SPF records.
  • ESP Migration: Migrating to a new ESP provides an opportunity to create a lean SPF record.
  • Prioritization: Prioritize essential sending sources within the SPF record's lookup limit.

Key considerations

  • ISP Forgiveness: Relying on ISP leniency is not a sustainable solution.
  • Bad Guidance: Be cautious of bad guidance from ESPs regarding SPF setup.
  • Ongoing Review: SPF record management requires continuous effort.
Expert view

Expert from Word to the Wise talks about migrating to a new ESP, that is a good opportunity to address the SPF record. Work with the new ESP to create a lean and optimized SPF record that only includes the necessary sending sources.

October 2022 - Word to the Wise
Expert view

Expert from Email Geeks explains that a significant problem is people publishing SPF for the wrong domain and ESPs providing bad guidance, recommending dedicated domains for the 5321.from.

July 2023 - Email Geeks
Expert view

Expert from Spamresource states that regularly reviewing and optimizing SPF records to remove obsolete entries is crucial. Also, consolidate includes where possible and ensure that the most important sending sources are prioritized within the 10-lookup limit.

May 2024 - Spamresource
Expert view

Expert from Email Geeks discusses the issue of overstuffed SPF records with too many DNS lookups, noting that ISPs seem to be forgiving despite the spec. Options considered are ignoring the issue or pushing clients to use different subdomains for different mail streams.

July 2022 - Email Geeks

What the documentation says
4Technical articles

Documentation emphasizes the 10 DNS lookup limit in SPF records, highlighting potential deliverability issues if exceeded. Suggested solutions include simplifying SPF records by removing unnecessary includes, utilizing alternative authentication methods like DKIM, and ensuring proper SPF, DKIM, and DMARC configuration and alignment. Utilizing DKIM can assist when SPF is problematic.

Key findings

  • 10 Lookup Limit: SPF records have a strict limit of 10 DNS lookups.
  • Deliverability Impact: Exceeding the lookup limit can negatively impact email deliverability.
  • DKIM Alternative: DKIM provides an alternative authentication method when SPF is problematic.
  • SPF, DKIM, DMARC: Proper configuration of SPF, DKIM, and DMARC is essential for email authentication.
  • DMARC Alignment: Alignment with DMARC ensures proper email deliverability.

Key considerations

  • Simplification: Regularly simplify SPF records by removing unnecessary includes.
  • Configuration: Ensure correct setup for all sending domains.
  • Authentication Combination: Leverage SPF, DKIM, and DMARC together for robust email authentication.
Technical article

Documentation from Microsoft answers that for Microsoft 365, it's essential to configure SPF, DKIM, and DMARC correctly. While SPF has its limits, combining it with DKIM can improve email deliverability and authentication. Ensure SPF is set up for all sending domains.

April 2022 - Microsoft
Technical article

Documentation from Google Workspace Admin Help explains that SPF records have a limit of 10 DNS lookups. Exceeding this limit can cause SPF checks to fail, impacting email deliverability. They suggest simplifying SPF records by removing unnecessary includes or using alternative authentication methods like DKIM.

August 2022 - Google Workspace Admin Help
Technical article

Documentation from DMARC.org recommends using both SPF and DKIM for email authentication and aligning them properly with DMARC. When SPF records are problematic, DKIM can provide an alternative authentication method, and the correct DKIM configuration with DMARC can allow you to achieve deliverability goals.

August 2024 - DMARC.org
Technical article

Documentation from RFC 7208 (SPF specification) specifies that SPF implementations MUST limit the number of DNS lookups performed during SPF evaluation to avoid denial-of-service attacks. The limit is set to 10 DNS lookups, including any lookups caused by 'include', 'a', 'mx', 'ptr', or 'exists' mechanisms.

January 2022 - RFC Editor