How do broken SPF records, like those with too many DNS lookups or exceeding size limits, affect email deliverability and authentication?
Matthew Whittaker
Co-founder & CTO, Suped
Published 30 Jun 2025
Updated 19 Aug 2025
6 min read
Email is a cornerstone of modern communication, from marketing campaigns to transactional notifications. For these messages to reach their intended recipients, robust email authentication is crucial. Sender Policy Framework (SPF) is one of the foundational standards designed to prevent email spoofing and ensure that emails originate from authorized servers.
However, an SPF record, while vital, can easily be misconfigured or become broken in ways that significantly harm your email deliverability and authentication rates. Two common culprits are exceeding the DNS lookup limit and creating records that are too large. These seemingly small technical details can have a ripple effect across your entire email ecosystem.
I'll explain what these broken SPF records mean, why they are problematic, and what steps you can take to identify and fix them, ensuring your legitimate emails consistently land in the inbox.
SPF records are DNS TXT records that list authorized sending IP addresses or domains. When an email server receives an email, it checks the sender's SPF record to verify if the sending server is legitimate. This process often involves DNS lookups, where the receiving server queries DNS to resolve the SPF record's various mechanisms, such as include, a, and mx.
The critical point here is that SPF records have a strict limit of 10 DNS lookups. This limit is defined in RFC 7208, the official SPF specification. Each time your SPF record includes a mechanism that requires a DNS query to resolve, it counts towards this limit. If your record requires more than 10 lookups, it becomes invalid. For more details on this, see how important is the 10 DNS lookups limit.
Beyond the lookup limit, there's also a record size limit. Your SPF record, including the domain name and the text of the record itself, should ideally fit within 512 octets for a UDP packet. Exceeding this can cause issues, as some DNS implementations might not correctly process larger records via UDP, potentially falling back to TCP or silently ignoring the record. This is especially relevant for older DNS systems or those without EDNS0 support.
SPF mechanisms that trigger DNS lookups
Mechanism
Description
Causes DNS lookup
a
Authorizes A records of the domain.
Yes
mx
Authorizes MX records of the domain.
Yes
ptr
Authorizes reverse DNS lookups. Discouraged.
Yes
include
Includes another domain's SPF record.
Yes
exists
Checks for the existence of an A record.
Yes
redirect
Points to another domain's SPF record for evaluation.
Yes
ip4
Authorizes an IPv4 address or range.
No
ip6
Authorizes an IPv6 address or range.
No
all
Defines the default policy for non-matching IPs.
No
Consider this example of an SPF record that is likely to exceed the 10-lookup limit:
Example of an SPF record exceeding lookup limitTXT
The direct impact on email deliverability and authentication
When your SPF record exceeds the lookup limit or is too large, it results in an SPF PermError. A PermError means the receiving mail server cannot correctly interpret your SPF record. This is a severe problem because it tells the recipient's server that your domain's authentication information is fundamentally flawed, not just that an email failed a check. This is different from a TempError, which indicates a temporary issue.
The impact of a PermError
When an SPF PermError occurs, the SPF check effectively fails. This is critical for DMARC (Domain-based Message Authentication, Reporting, and Conformance), which relies on SPF and DKIM for email authentication. If SPF fails due to a PermError, and DKIM also fails or is not aligned, your emails will fail DMARC authentication. For more information, read what does it mean when SPF is not aligned.
When DMARC fails, based on your DMARC policy (p=none, p=quarantine, or p=reject), receiving servers may:
Reject the email: The email is entirely blocked and never reaches the recipient.
Quarantine the email: The email is delivered to the spam or junk folder, where it's unlikely to be seen.
Deliver it normally: This happens with a p=none policy, but it still negatively impacts your domain's reputation.
Even a p=none DMARC policy, which doesn't enforce delivery actions, will still report SPF authentication failures. These reports are crucial for understanding how your emails are being perceived by receiving mail servers. Ignoring these PermErrors can lead to a degraded sender reputation over time, resulting in more emails being marked as spam or rejected, even if other authentication methods pass.
Moreover, if your SPF record exceeds the size limit, some mail servers might silently ignore it. This means your SPF authentication essentially becomes non-existent, leaving your domain vulnerable to spoofing and increasing the likelihood of your legitimate emails landing in the spam folder or on an email blacklist (or blocklist). For more, read the SPF lookup limit explained.
Identifying and resolving broken SPF records
The first step to fixing a broken SPF record is to identify the issue. You can use various online tools to check your domain's SPF record and see if it returns a PermError for lookups or size. The challenge often lies in consolidating multiple sending services into a single, compliant SPF record.
The most effective solution for exceeding the 10-lookup limit is often SPF flattening. This involves replacing include mechanisms with the actual IP addresses they resolve to, reducing the number of DNS lookups. However, this requires regular maintenance as IP addresses used by third-party senders can change. For a detailed guide on remediation, see how to fix SPF record exceeding lookup limit.
Broken SPF record
Your SPF record uses too many include statements, resulting in over 10 DNS lookups, or its overall length exceeds the recommended 512 octet limit. This leads to an SPF PermError.
Impact
Emails originating from authorized sources may fail SPF authentication, consequently leading to DMARC failure. This significantly increases the likelihood of emails being sent to spam, quarantined, or outright rejected by recipient mail servers. Your domain's sender reputation can also be severely damaged, making it harder to reach the inbox in the future.
Optimized SPF record
Your SPF record adheres to the 10-DNS-lookup limit and the size limit by consolidating include mechanisms, removing redundant entries, or using SPF flattening techniques. The record is valid and correctly interpreted by receiving servers.
Benefit
Consistent SPF authentication, leading to DMARC pass rates. This ensures that authorized emails are delivered to the inbox, maintains a strong sender reputation, and protects your domain from phishing and spoofing attempts. Improved email deliverability means better engagement and conversion rates for your email campaigns.
Other strategies include removing unnecessary ptr mechanisms, which are often deprecated and consume lookups, and consolidating multiple include statements from the same vendor if they offer a single, overarching include that covers all their sending IPs. Remember, every includemechanism counts as a DNS lookup.
Proactive maintenance for ongoing deliverability
Maintaining a healthy SPF record is an ongoing process, not a one-time fix. As your organization adopts new email sending services, or as existing vendors update their infrastructure, your SPF record may need adjustments. Regularly monitoring your SPF and DMARC reports is essential to catch these issues before they significantly impact your deliverability. If you need assistance with DMARC, see how to troubleshoot DMARC failures.
A robust email authentication setup, including a properly configured SPF record alongside DKIM and DMARC, is the best defense against email spoofing and phishing attempts. It also signals to internet service providers (ISPs) that your emails are legitimate, which is crucial for maintaining a positive sender reputation and avoiding blacklists (or blocklists). This helps ensure your emails are consistently delivered to the inbox, enhancing trust and engagement with your recipients.
Key takeaways for SPF compliance
Adhere to limits: Always keep your SPF record within the 10 DNS lookup limit and the size limit (ideally 450-512 octets).
Consolidate: If using multiple third-party senders, seek opportunities to consolidate include statements or use SPF flattening.
Monitor regularly: Continuously monitor your DMARC reports for SPF PermErrors and address them promptly.
Combine with other standards: SPF works best when used in conjunction with DKIM and DMARC for comprehensive email authentication.
Views from the trenches
Best practices
Always aim to keep your SPF record concise and under the 10-lookup limit.
Regularly review your SPF record, especially after adding new email services, to prevent issues.
Implement DMARC with a monitoring policy (p=none) to receive reports on SPF failures.
Consider using an automated SPF flattening service if you have many third-party includes.
Prioritize SPF and DKIM authentication for all your sending domains and subdomains.
Common pitfalls
Ignoring the 10 DNS lookup limit, leading to SPF PermError and DMARC failures.
Adding too many 'include' mechanisms from various ESPs or SaaS tools.
Creating SPF records that exceed the recommended UDP packet size (512 octets).
Failing to regularly audit SPF records after changes in email infrastructure.
Relying solely on SPF without also implementing DKIM and DMARC for complete authentication.
Expert tips
If your IT department is hesitant, present the RFC 7208 documentation on SPF limits.
Highlight how DMARC compliance and BIMI (Brand Indicators for Message Identification) require proper SPF setup.
Emphasize the direct link between a valid SPF record and improved sender reputation, leading to better inbox placement.
Show the potential cost savings from reduced spam complaints and customer service inquiries.
Explain that some providers (e.g., Microsoft) might have hidden SPF DNS timeouts.
Marketer view
Marketer from Email Geeks says they have experienced a direct impact on deliverability from SPF issues, although it was difficult to pinpoint the exact cause at the time.
2018-01-15 - Email Geeks
Marketer view
Marketer from Email Geeks says that SPF failures typically result in a slight increase in soft bounces, which can be bothersome but not catastrophic.
2019-03-20 - Email Geeks
Ensuring your emails get through
Broken SPF records, whether due to too many DNS lookups or exceeding size limits, pose a significant threat to email deliverability and authentication. These errors can lead to your legitimate emails being marked as spam, rejected, or failing DMARC, ultimately impacting your communication efforts and sender reputation.
By understanding the strict limits SPF imposes and proactively monitoring and optimizing your records, you can ensure your emails consistently reach the inbox, maintain strong authentication, and protect your domain's integrity. It's a critical component of any successful email strategy.
