What is the maximum number of DNS lookups allowed in an SPF record?
Michael Ko
Co-founder & CEO, Suped
Published 14 Jun 2025
Updated 18 Oct 2025
7 min read
When you send emails, you want them to reach their intended recipients. A crucial part of ensuring this happens is proper email authentication, and SPF (Sender Policy Framework) is a cornerstone of this process. SPF works by allowing domain owners to publish a DNS TXT record that lists all the IP addresses and mail servers authorized to send emails on behalf of their domain. Receiving mail servers then check this record to verify incoming mail, reducing spam and phishing attempts.
However, SPF records aren't limitless. They come with a specific constraint known as the DNS lookup limit. This limit is in place to prevent abuse and ensure efficient processing by email servers. Exceeding this limit can cause significant deliverability issues, essentially making your legitimate emails look suspicious and more likely to be sent to spam folders or blocked entirely.
Understanding this limit and how to manage it is essential for anyone responsible for email deliverability. Misconfigurations can lead to authentication failures, impacting your sender reputation and overall email program effectiveness. Let's delve into what this limit is and why it matters.
Understanding the SPF DNS lookup limit
The maximum number of DNS lookups allowed in an SPF record is 10. This limit is explicitly defined in Section 4.6.4 of the SPF RFC 7208, which states that an SPF-compliant email receiver must not perform more than 10 DNS lookups when evaluating an SPF record. This includes lookups triggered by mechanisms like a, mx, ptr, exists, and include statements.
It's important to note that direct IP addresses, such as ip4 or ip6 mechanisms, do not count towards this DNS lookup limit because they do not require a DNS query. This distinction is crucial when optimizing your SPF record.
Many email service providers (ESPs) and third-party senders require you to include their domains in your SPF record. Each include statement itself counts as one DNS lookup. If that included domain then itself includes another domain, that's another lookup. This chain of lookups can quickly exhaust your limit if not managed carefully.
Why the 10-lookup limit exists
The 10-lookup limit isn't an arbitrary number. It's a pragmatic restriction designed to prevent performance issues and potential denial-of-service (DoS) attacks on DNS servers. When a receiving mail server processes an SPF record, it needs to perform DNS queries for each mechanism that requires a lookup (like include, a, or mx). Each query takes time and consumes resources.
Without this limit, a malicious sender could craft an SPF record that triggers an excessive number of DNS queries, potentially slowing down mail servers or even crashing them through a recursive lookup loop. The 10-lookup rule provides a reasonable balance between flexibility for legitimate senders and protection against abuse.
RFC definition of DNS lookup
According to RFC 7208 (Section 4.6.4), a DNS lookup is defined as a query for an A, MX, PTR, or TXT record. This explicitly excludes ip4 and ip6 mechanisms, as they contain literal IP addresses that do not require further DNS resolution.
Knowing exactly what counts as a lookup is fundamental to correctly configuring your SPF record and avoiding authentication failures. It's a common oversight that leads to email delivery problems.
Impact of exceeding the SPF lookup limit
Exceeding the 10-DNS lookup limit can have severe consequences for your email program. When a receiving server encounters an SPF record that requires more than 10 lookups, it treats the SPF record as invalid. This usually results in a PermError (Permanent Error). A PermError signals to the receiving server that SPF authentication has failed.
The immediate impact of an SPF PermError is a degradation of your email deliverability. Emails are more likely to be marked as spam, quarantined, or outright rejected. This can lead to decreased engagement, missed communications, and damage to your sender reputation. While some receivers might still deliver the email, relying on this is risky and unpredictable.
Consequences of exceeding the limit
Reduced deliverability: Emails are more likely to land in spam folders or be rejected by receiving servers.
Damaged sender reputation: Consistent SPF failures negatively affect how mail providers perceive your domain.
Authentication failures: SPF PermError leads to a failed SPF check, impacting DMARC results.
How to identify the issue
DMARC reports: Aggregate and forensic reports provide insights into SPF authentication results, including PermError failures.
Bounce messages: Some bounce messages will explicitly state SPF authentication failures or PermError issues.
SPF record checkers: Online tools can validate your SPF record and detect lookup limit breaches.
To effectively monitor for and diagnose these issues, a robust DMARC monitoring solution is invaluable. It provides the visibility you need into your email authentication results, allowing you to proactively address SPF lookup limit breaches and other technical issues that affect your deliverability.
Strategies for managing SPF lookups
Dealing with an overstuffed SPF record requires a strategic approach. The goal is to reduce the number of DNS lookups without compromising the authenticity of your legitimate sending sources. Here are some effective strategies:
Consolidate includes: If you're using multiple email sending services, check if any of them share underlying infrastructure that can be represented by a single include statement. This is often the case with large providers.
Use IP addresses directly: For known, stable IP addresses of your sending servers, use ip4 or ip6 mechanisms instead of a or include. Remember, these do not count towards the 10-lookup limit.
Remove unused entries: Audit your SPF record regularly and remove any mechanisms or includes for services you no longer use. This is a quick win for reducing lookups.
Utilize SPF flattening: This advanced technique involves resolving all include statements to their underlying IP addresses at regular intervals and maintaining the flat list in your SPF record. This reduces multiple lookups to a single one. Suped offers a robust SPF flattening solution to automate this process and ensure your record stays within limits.
When optimizing your SPF record, remember that each include can hide several additional lookups. For instance, an include:thirdparty.com might itself contain a and mx mechanisms, plus other include statements, quickly pushing you over the limit. This nested lookup problem is what makes SPF flattening so valuable.
Example of a complex SPF record that could exceed the limitDNS
Regularly checking your SPF record for compliance with the 10-lookup limit is a critical step in maintaining healthy email deliverability. Tools that provide SPF monitoring can alert you to potential issues before they cause significant email disruptions.
Ensuring email deliverability
Maintaining a healthy SPF record that adheres to the 10-DNS lookup limit is not just a technical detail, it's a fundamental aspect of effective email deliverability and security. By carefully auditing your record, consolidating entries, utilizing IP addresses directly, and employing advanced techniques like SPF flattening, you can ensure your emails are authenticated correctly.
Ignoring this limit can lead to SPF PermErrors and significantly reduce your inbox placement rates, costing you time, resources, and potentially lost business. Proactive management and ongoing monitoring are key to preventing these issues.
To effectively manage your SPF record and ensure compliance with the 10-lookup limit, consider leveraging a comprehensive email security and deliverability platform like Suped. Our platform offers not just DMARC monitoring but also AI-powered recommendations, real-time alerts, and automated SPF flattening to keep your email authentication robust and your emails landing in the inbox.
