What are the options for dealing with overstuffed SPF records exceeding DNS lookup limits?
Matthew Whittaker
Co-founder & CTO, Suped
Published 24 Jul 2025
Updated 16 Aug 2025
7 min read
Managing Sender Policy Framework (SPF) records can be a complex task, especially when dealing with multiple email sending services. A common challenge arises when an SPF record exceeds the 10-DNS lookup limit, leading to a PermError. While some mail receivers, such as Google and Yahoo, might seem more forgiving with these oversized records, relying on this leniency is not a sustainable or recommended strategy for consistent email deliverability.
Many organizations face this dilemma because the complexity of their email infrastructure often makes it difficult to trim down the SPF record without impacting legitimate sending sources. This article explores practical options and advanced solutions to manage SPF records that exceed DNS lookup limits, ensuring your emails reach their intended inboxes.
The SPF specification (RFC 7208) states that SPF records must not require more than 10 DNS lookups that resolve SPF records (e.g., a, mx, ptr, and include). Exceeding this limit results in an SPF PermError, indicating that the SPF check cannot be completed reliably. This often leads to legitimate emails being flagged as spam or rejected outright. Understanding how important this limit is is the first step toward resolution.
Each time your SPF record includes another domain or IP range that requires a DNS query, it counts towards this limit. For instance, an include mechanism for an email service provider (ESP) will trigger a lookup, and if that ESP's SPF record also contains includes, those nested lookups contribute to your domain's total. This can quickly accumulate, especially for organizations using multiple third-party sending services.
When your SPF record is broken by exceeding the lookup limit, recipients' mail servers can't fully validate senders, raising spam flags. While major providers might sometimes overlook this, it's not a guarantee and can lead to inconsistent deliverability, with some emails landing in spam folders.
Manual optimization strategies
Before exploring advanced solutions, it's crucial to optimize your existing SPF record. The goal is to reduce the number of DNS lookups to stay within the limit. This often involves a careful review of all mechanisms and consolidating where possible.
Remove unused services: Start by identifying and removing any email sending services or domains that are no longer in use. This is a common culprit for bloated SPF records.
Replace domain mechanisms with IP addresses: If a service uses a stable set of IP addresses, you can replace include, a, or mx mechanisms with direct ip4 or ip6 ranges. This eliminates a DNS lookup. However, this requires diligent monitoring of the ESP's IP ranges to prevent future SPF failures, as these can change without notice.
Consolidate multiple SPF records: While you can only have one SPF TXT record per domain, you can sometimes consolidate the underlying mechanisms. Review services to see if their SPF includes overlap or if you can use broader, single includes for multiple services from the same vendor.
These manual adjustments can help fix an SPF record exceeding the lookup limit. However, they require ongoing maintenance as sending IP addresses or services change, which can be a significant operational burden.
Best practices for manual SPF management
Regular audits: Periodically review your SPF record and all included domains. Remove outdated or unused entries to keep the record lean. Many mailhardener.com and dmarcly.com advise on this process.
DNS TXT record length: Be mindful of the 255-character limit for individual DNS TXT strings. If your SPF record gets too long, it may need to be split into multiple strings, though this doesn't affect DNS lookups. For more on this, review why your SPF record is too long.
Advanced solutions and tools
When manual optimization isn't sufficient or becomes too cumbersome, more advanced solutions are necessary. These typically involve restructuring your domain's email sending strategy or using tools to dynamically manage your SPF record.
Using subdomains for segmentation
One effective method is to use dedicated subdomains for different mail streams or sending platforms. Instead of sending all email from your primary domain (e.g., example.com), you can designate subdomains like marketing.example.com for marketing emails and transactions.example.com for transactional alerts. Each subdomain can then have its own SPF record tailored to the specific sending services used for that stream, effectively segmenting and reducing the lookup count for any single record. This is a best practice for SPF and subdomain usage.
SPF flattening
SPF flattening involves converting all include mechanisms into direct ip4 and ip6 mechanisms. This reduces your SPF record to a single DNS lookup, as all IP addresses are explicitly listed. You can learn when SPF flattening is needed and how it works.
Manual flattening requires regularly checking your ESPs' SPF records for changes in their IP ranges and updating your flattened record accordingly. This can be time-consuming and error-prone. Another issue that can arise with flattening is the CharacterStringTooLong error.
Manual flattening
Process: Manually extract all IP ranges from included SPF records and add them directly to your domain's SPF record. This involves resolving all nested includes yourself.
Maintenance: Requires vigilant monitoring of all included services for IP address changes. Any change necessitates a manual update to your SPF record.
Flexibility: Low. Becomes burdensome with many sending services or frequently changing IPs. Prone to human error.
Automated SPF flattening services
Process: A third-party service, like AutoSPF, monitors your original SPF record and provides a single, dynamic SPF record that always reflects the current IP ranges of all your services. This is sometimes called hosted SPF.
Maintenance: Automated. The service handles all updates, reducing manual effort and potential errors. We've compiled best practices for using SPF flatteners.
Flexibility: High. Ideal for organizations with many ESPs or dynamic IP ranges. Offers peace of mind regarding SPF compliance.
Leveraging DMARC and DKIM for resilience
While SPF is crucial, it's part of a broader email authentication ecosystem that includes DomainKeys Identified Mail (DKIM) and Domain-based Message Authentication, Reporting, and Conformance (DMARC). Leveraging these together offers a more robust defense against email spoofing and improves deliverability, even if SPF encounters issues.
DMARC allows you to tell receiving mail servers how to handle emails that fail SPF or DKIM checks, and it also provides reporting on authentication results. If your SPF record exceeds the lookup limit, a strong DKIM signature can still pass authentication for DMARC. This is why implementing DMARC with a policy of p=quarantine or p=reject is essential, as it adds a layer of resilience to your email deliverability, even if SPF validation fails due to an overstuffed record. To ensure your SPF record is properly formatted and does not cause issues with the DNS lookup limit, you can refer to how to format SPF TXT records.
It is important to understand how SPF 'a' records affect DNS lookups as they also contribute to the 10-lookup limit. When managing your SPF, ensure that all mechanisms, including a and mx, are accounted for within the limit to prevent authentication failures.
Views from the trenches
Best practices
Actively audit and remove outdated SPF 'include' mechanisms from your record regularly to prevent bloating.
Utilize subdomains for different mail streams to segregate SPF records and keep each one under the 10-lookup limit.
Implement automated SPF flattening services to manage dynamic IP addresses from ESPs without manual intervention.
Always combine SPF with DKIM and DMARC for comprehensive email authentication and robust deliverability.
Common pitfalls
Ignoring the SPF 10-DNS lookup limit, assuming major ISPs will always be forgiving, which can lead to sporadic deliverability issues.
Manually flattening SPF records without a robust system for tracking and updating ESP IP address changes.
Placing SPF records for third-party sending services on your bare domain when a dedicated subdomain would be more appropriate.
Underestimating the complexity of SPF issues, leading to a false sense of security regarding email authentication.
Expert tips
Consider that SPF was designed for a different era of email infrastructure; modern needs often push its limits.
While the SPF specification might not be updated soon, strategic use of subdomains and automated flattening are practical current solutions.
Focus on a comprehensive authentication strategy with DMARC and DKIM, as they offer greater resilience even if SPF has issues.
Don't overlook the potential for a 'CharacterStringTooLong' error, especially when flattening your SPF record with many IP ranges.
Marketer view
Marketer from Email Geeks says many clients rely solely on DKIM to avoid SPF lookup limit issues, and SPF flattening is a viable option, whether through providers or self-hosted solutions.
2022-07-25 - Email Geeks
Marketer view
Marketer from Email Geeks says that while subdomains are generally good, they aren't always suitable, especially when organizations need to send many different email types from the same core address, like `support@example.com`.
2022-07-25 - Email Geeks
Navigating the SPF landscape
Dealing with overstuffed SPF records and the 10-DNS lookup limit is a prevalent challenge in email deliverability. While some major mail providers may exhibit a degree of forgiveness, adhering to the SPF specification is critical for consistent inbox placement and strong email authentication. Ignoring the limit can lead to emails being misclassified as spam, impacting your communication efforts and sender reputation.
By strategically implementing solutions such as subdomain segmentation and automated SPF flattening, you can effectively manage your SPF records, ensuring they remain compliant and your emails are properly authenticated. Combining these practices with robust DKIM and DMARC implementations provides a comprehensive defense, enhancing overall email security and deliverability.
Google and 
Yahoo, might seem more forgiving with these oversized records, relying on this leniency is not a sustainable or recommended strategy for consistent email deliverability.
