How can I optimize my SPF record to stay within the lookup limit when using multiple email sending services?
Michael Ko
Co-founder & CEO, Suped
Published 1 Jul 2025
Updated 17 Aug 2025
9 min read
Many organizations rely on multiple email sending services for different purposes, like marketing, transactional emails, and internal communications. While this offers flexibility, it often leads to challenges with SPF (Sender Policy Framework) records, specifically hitting the 10 DNS lookup limit. Exceeding this limit can cause legitimate emails to fail SPF authentication, impacting your email deliverability and potentially leading to messages landing in spam or being rejected. I've seen this issue firsthand, and it's a common stumbling block for businesses trying to maintain a robust email infrastructure.
The SPF specification (RFC 7208) dictates that an SPF record must not cause more than ten DNS lookups that resolve to an A, MX, PTR, or SPF include mechanism. This limit exists to prevent denial-of-service (DoS) attacks on DNS infrastructure. Each time an include mechanism, an a mechanism (if it specifies a domain name), or an mx mechanism is present, a DNS query is triggered. When the total number of these lookups exceeds ten, mail servers may treat your SPF record as a PermError, leading to authentication failures.
It's important to understand that not all mechanisms count towards this limit. Mechanisms like ip4, ip6, all, and redirect do not trigger additional DNS lookups. However, if you have a long list of include statements for various email service providers (ESPs) or a records pointing to hostnames, you can quickly hit this ceiling. For example, a single include from a major ESP might itself contain multiple nested includes, consuming several lookups from your quota.
Hitting the SPF lookup limit means that receiving mail servers might not be able to fully validate your SPF record, regardless of whether the sending IP is actually authorized. This can result in legitimate emails being marked as spam or rejected outright, severely impacting your communication efforts and sender reputation. This is why it's crucial to optimize your SPF record, especially when using several email sending services. For a deeper dive, consider understanding how important the 10 DNS lookups limit on SPF records truly is.
Initial optimization strategies
When faced with an SPF record exceeding the 10-lookup limit, several strategies can help you optimize it. The primary goal is to reduce the number of DNS lookups while ensuring all legitimate sending sources are authorized. This often involves careful auditing and restructuring of your SPF record.
One effective method is to audit your existing SPF record and remove any unnecessary entries. Over time, businesses might change email providers or discontinue services, but their SPF records are not always updated accordingly. Many vendors might also advise you to add unnecessary entries to your SPF. If your domain isn't in the return path (Mail From address or Envelope From), you might not need an SPF include for that vendor. Always verify the Return-Path or Mail From address used by your services. For insights on incorrect SPF advice, consider this external resource.
Another approach involves consolidating your SPF record. If an ESP provides multiple include mechanisms, check if there's a single, more comprehensive include that covers all necessary IPs without redundant lookups. Alternatively, if a service uses fixed IP ranges, you can replace their include mechanism with direct ip4 or ip6 entries in your SPF record, which do not count towards the 10-lookup limit. However, this requires diligent monitoring, as IP addresses can change. For a comprehensive guide on managing SPF records and avoiding DNS size issues, see how to format SPF TXT records.
Regular review is key to preventing SPF errors. Proactive management of your SPF record helps prevent it from becoming too long or exceeding the limit. Understanding options for dealing with overstuffed SPF records is essential for maintaining optimal email deliverability.
Traditional SPF Challenges
Complex: Difficult to manage with many services due to nested includes.
Exceeds Limits: Prone to hitting the 10-DNS lookup limit with numerous include statements.
Deliverability Risk: Higher chance of emails failing authentication and landing in spam.
Optimized SPF Solutions
Simpler Management: Clearer structure, easier to maintain and update.
Within Limits: Achieved through consolidation, direct IPs, or strategic subdomains.
Improved Deliverability: Enhanced authentication leads to better inbox placement and trust.
Advanced techniques for complex setups
For more complex scenarios, especially when you have many email sending services, advanced techniques become necessary. SPF flattening is a popular workaround, where include mechanisms are converted into a static list of IP addresses or IP ranges. While this reduces DNS lookups to zero for those flattened entries, it introduces a new challenge: maintenance. As IP addresses change, your flattened record needs to be manually updated, or your email authentication will eventually break. You can find more about SPF flattening explained in this external resource.
Using subdomains for different sending services is another robust strategy. Instead of having a single, sprawling SPF record on your root domain, you can assign a unique subdomain to each major sending service. For example, your marketing emails could be sent from marketing.yourdomain.com, while transactional emails come from transactions.yourdomain.com. Each subdomain would then have its own SPF record, containing only the include mechanisms relevant to its specific sending service. This effectively distributes the lookup burden across multiple SPF records, each with its own 10-lookup limit. You can learn more about configuring DNS records for multiple ESPs using subdomains.
While SPF macros offer a degree of flexibility, they are generally less common and more complex to implement correctly. They allow for dynamic SPF checks based on parts of the email address, which could potentially help in very specific, custom setups to manage lookups. However, for most organizations, the strategies of auditing, consolidating, flattening, or using subdomains are more practical and effective.
To effectively optimize your SPF record, it's essential to regularly audit it. This proactive approach helps identify unnecessary entries or outdated includes that contribute to exceeding the lookup limit. You should also regularly check your SPF record for validity and compliance. If you see errors like "too many lookups" or a blocklist (or blacklist) listing due to SPF issues, it's a clear sign that action is needed. These errors can be detected using a email deliverability tester.
When troubleshooting, pay close attention to the Return-Path (also known as the Mail From or Envelope From) address in your email headers. This is the domain that SPF checks against, not necessarily the From address displayed in email clients. Many third-party services, such as Shopify or Mailgun, often handle SPF authentication on their own subdomains or through their configured return paths, meaning you might not need to include their main SPF record in your root domain's SPF. For example, if Shopify sets up a return path on a subdomain via Sendgrid, then SPF is handled by that subdomain's record. You can find more details on how SPF and DKIM work with services like Shopify.
Implementing these optimizations requires careful planning to avoid disrupting your email flow. Always test changes to your DNS records thoroughly. SPF record issues can significantly impact email deliverability, leading to your messages being blocked or flagged as spam. For more on this, check out how to troubleshoot SPF authentication issues with various ESPs.
When adding SPF entries, carefully consider if you can use direct IP addresses (ip4 or ip6) instead of include mechanisms. Using direct IPs eliminates DNS lookups, helping you stay within the limit. However, this demands regular checks to ensure the IPs have not changed. Learn more about the best practice for using IP addresses in SPF records.
The Return-Path domain is key
SPF authentication checks the Return-Path (also known as Mail From or Envelope From) domain of your email, not the visible From address. Many ESPs handle SPF via their own subdomains or return paths. Always verify the Return-Path to see if you genuinely need to include their SPF in your primary domain's record, which can save valuable DNS lookups.
Maintaining SPF record health
Optimizing your SPF record to stay within the 10-lookup limit is a critical step for ensuring email deliverability, especially when leveraging multiple email sending services. By systematically auditing your existing record, removing obsolete entries, leveraging direct IP addresses where possible, or strategically using subdomains, you can prevent authentication failures. The goal is a lean, accurate SPF record that effectively authorizes your legitimate senders without incurring PermError due to excessive DNS lookups. Regular monitoring and proactive management are essential to maintain your domain’s email authentication and protect your sender reputation.
Views from the trenches
Best practices
Regularly audit your SPF record to remove any services no longer in use, ensuring it remains lean and accurate.
Verify the return-path domain (Mail From or Envelope From) of your email sending services before adding their SPF includes.
Consolidate SPF entries where providers offer a single, comprehensive include that covers all necessary IPs without redundancy.
Consider using subdomains for different email sending services to manage lookup limits more effectively across multiple records.
If using SPF flattening, implement a robust process to ensure continuous updates for any changes in IP addresses.
Common pitfalls
Blindly adding every SPF include recommended by vendors, even if unnecessary for your specific email setup.
Assuming that only the 11th lookup will fail while earlier ones pass; an invalid SPF record can cause complete authentication failure.
Neglecting to update flattened SPF records when service providers change their IP ranges, leading to broken authentication.
Not checking the Return-Path or Mail From address, which is the actual domain SPF authenticates, leading to incorrect inclusions.
Having multiple SPF records for the same domain, which is a significant configuration error and will cause issues.
Expert tips
Utilize SPF macros for advanced, dynamic SPF configurations if you have very specific and complex email routing needs.
Review email headers, specifically the 5321.From address, to understand which domain SPF truly applies to for each sender.
Recognize that some ESPs, like Shopify and Mailgun, often use subdomains for their return paths, reducing the need for root domain SPF inclusions.
Prioritize maintaining a valid SPF record over trying to force too many lookups, as invalid records result in outright failures.
Regularly check your SPF record for validity after making any changes to ensure it complies with the 10-lookup limit.
Expert view
Expert from Email Geeks says: The importance of staying within the SPF lookup limit depends on where the required IP addresses are located within the SPF tree. If an authorized IP is found before the 10-lookup threshold, the email might still pass.
2024-02-10 - Email Geeks
Marketer view
Marketer from Email Geeks says: It is important for an SPF record to be valid and only list the necessary IP addresses. One should definitely consider SPF flattening, remove unnecessary entries, and explore SPF macros if feasible.
Shopify or 
Mailgun, often handle SPF authentication on their own subdomains or through their configured return paths, meaning you might not need to include their main SPF record in your root domain's SPF. For example, if Shopify sets up a return path on a subdomain via 
Sendgrid, then SPF is handled by that subdomain's record. You can find more details on how SPF and DKIM work with services like Shopify.
