--- title: "Why Sender Policy Framework (SPF) Has a Lookup Limit of 10? | AutoSPF" description: "SPF helps recipients’ mailboxes verify the authenticity of senders’ domains by referring to their predefined policies." image: "https://autospf.com/og/blog/why-sender-policy-framework-spf-has-a-lookup-limit-of-10.png" canonical: "https://autospf.com/blog/why-sender-policy-framework-spf-has-a-lookup-limit-of-10/" --- Quick Answer SPF helps recipients’ mailboxes verify the authenticity of senders’ domains by referring to their predefined policies. To do this, the receiving server retrieves the SPF record linked to the sender’s domain. A standard SPF record consists of one or more mechanisms (like ip4, ip6, include, mx, etc.) that specify which IP addresses and domains are officially authorized to send emails. ## Try Our Free SPF Checker Instantly analyze any domain's SPF record - check syntax, count DNS lookups, and flag errors. [ Check SPF Record → ](/tools/spf-checker/) Share [ ](https://www.linkedin.com/sharing/share-offsite/?url=https%3A%2F%2Fautospf.com%2Fblog%2Fwhy-sender-policy-framework-spf-has-a-lookup-limit-of-10%2F "Share on LinkedIn") [ ](https://twitter.com/intent/tweet?text=Why%20Sender%20Policy%20Framework%20%28SPF%29%20Has%20a%20Lookup%20Limit%20of%2010%3F&url=https%3A%2F%2Fautospf.com%2Fblog%2Fwhy-sender-policy-framework-spf-has-a-lookup-limit-of-10%2F "Share on X/Twitter") [ ](https://www.facebook.com/sharer/sharer.php?u=https%3A%2F%2Fautospf.com%2Fblog%2Fwhy-sender-policy-framework-spf-has-a-lookup-limit-of-10%2F "Share on Facebook") [ ](https://reddit.com/submit?url=https%3A%2F%2Fautospf.com%2Fblog%2Fwhy-sender-policy-framework-spf-has-a-lookup-limit-of-10%2F&title=Why%20Sender%20Policy%20Framework%20%28SPF%29%20Has%20a%20Lookup%20Limit%20of%2010%3F "Share on Reddit") [ ](mailto:?subject=Why%20Sender%20Policy%20Framework%20%28SPF%29%20Has%20a%20Lookup%20Limit%20of%2010%3F&body=Check out this article: https%3A%2F%2Fautospf.com%2Fblog%2Fwhy-sender-policy-framework-spf-has-a-lookup-limit-of-10%2F "Share via Email") ![mail server](https://media.mailhop.org/autospf/images/2024/04/spf-validator-4167.jpg) SPF helps recipients’ mailboxes verify the authenticity of senders’ domains by referring to their predefined policies. To do this, the receiving server retrieves the SPF record linked to the sender’s domain. A standard [SPF record](/explaining-sender-policy-framework-spf-macros/spf-record-syntax/) consists of one or more mechanisms (like ip4, ip6, include, mx, etc.) that specify which IP addresses and domains are officially authorized to send emails on the domain owner’s behalf. > “From an engineering perspective, the 10-lookup limit is a resource protection mechanism, not a security feature,” says Adam Lundrigan, CTO of DuoCircle. “RFC 7208 caps lookups to prevent SPF evaluation from becoming a DNS amplification vector. But the practical effect is that any enterprise using more than 3-4 email services hits the wall. The fix is either flattening - which trades lookup count for record length - or macros, which delegate resolution entirely.” > “The 10-lookup limit is the single most common reason enterprise SPF records silently break,” says Brad Slavin, General Manager of DuoCircle and founder of AutoSPF. “In our experience managing SPF for 2,000+ customer domains, the failure mode is always the same: a team adds a new SaaS tool, its include pushes the total past 10, and legitimate email starts failing - but nobody notices until a customer complains about missing invoices or password resets.” _Per [RFC 7208](https://datatracker.ietf.org/doc/html/rfc7208), SPF evaluation is capped at 10 DNS mechanism lookups and 2 void lookups per check - exceeding either limit produces a `PermError` that fails authentication for every message from the domain._ Once the SPF record is retrieved, the recipient’s mail server evaluates it to determine whether the sender’s IP address is allowed to send emails to the specified domain. The email passes the [SPF authentication check](/spf-validation-failed-meaning-and-troubleshooting-methods/) if the sender’s IP address matches one of the authorized entries in the SPF record. Otherwise, if the sender’s IP address is not listed or is listed as unauthorized, the email may be marked as suspicious or rejected, depending on the recipient’s [email server configuration](https://www.manageengine.com/products/support-center/help/adminguide/introduction/mail-server-settings.html#:~:text=Mail%20Server%20Settings%20%26%20Mail%20Configuration&text=Server%20Name%2FIP%20Address%3A%20Denotes,or%20POP%20and%20so%20on%29). However, there is a lookup limit of 10, which is a headache for domain owners, especially the ones with intricate and extensive email infrastructures. If your SPF record has also reached the maximum lookup limit, try [SPF flattening](/). _It’s a technique to resolve this issue by compressing all the domains within the SPF, eliminating the need for frequent DNS lookups._ ![email server](https://media.mailhop.org/autospf/images/2024/04/spf-permerror-2.jpg) But why does this limit even exist? Well, this restriction prevents overburdening resources and blocks [phishing attempts](https://www.bankinfosecurity.com/phishing-attacks-targeting-political-parties-germany-warns-a-24784). Let’s understand this better. ## Reasons Why the Lookup Limit Exists ### DNS Query Overhead When recipients’ servers retrieve SPF records, they send queries to DNS that sometimes involve multiple lookups. If unlimited lookups were allowed, the [DNS server](https://www.geeksforgeeks.org/working-of-domain-name-system-dns-server/) would get overloaded, leading to technical issues and frequent instances of false positives or negatives. ### Network Latency [Excessive DNS lookups](/blog/solving-the-too-many-dns-lookup-error/) can introduce network latency, causing delays in email delivery. This delay can negatively impact the user experience, especially in time-sensitive communications. _Also, spam filters consider high [network latency](https://www.techtarget.com/whatis/definition/latency) as an indicator of poorly configured or malicious servers_. This triggers recipients’ mailboxes to mark your emails as spam or reject them outright, irrespective of SPF results. Network latency also affects the [SMTP handshake process](https://study.com/academy/lesson/simple-mail-transfer-protocol-definition-uses.html#:~:text=Once%20the%20individual%20selects%20'send,the%20message%20will%20be%20deliverable.), which involves securing a connection between the sending and receiving mail servers. ### Resource Consumption _DNS servers have finite resources, including bandwidth, processing power, and memory_. Allowing unlimited [SPF lookups](/spf-too-many-dns-lookups/spf-lookup/) could strain DNS servers, leading to resource exhaustion and potential service disruptions. ### Prevention Against DDoS Attacks Multiple SPF lookups allow [threat actors to exploit vulnerable DNS servers](https://gbhackers.com/critical-dnssec-flaw/) by crafting spoofed SPF lookup requests with the recipient’s IP address as the source. The DNS server then sends large responses to the victim’s IP address, significantly increasing the volume of traffic directed at the victim and potentially leading to a [DDoS scenario](https://en.wikipedia.org/wiki/Denial-of-service%5Fattack). ### Complexity If unlimited SPF lookups were allowed, [email processing algorithms](https://www.tributemedia.com/blog/email-algorithms) would have been far more complex and dynamic, making it challenging for administrators to manage SPF records. Moreover, a higher lookup limit invites vulnerabilities and bugs, whereas limited lookups help email servers implement simpler and more efficient [SPF validation](/spf-validation-failed-meaning-and-troubleshooting-methods/spf-validation-error/) mechanisms. ![email service](https://media.mailhop.org/autospf/images/2024/04/spf-validator-4168.jpg) ## Wrapping it The limit of 10 SPF lookups aligns with industry best practices and recommendations. It strikes a balance between [email security](/10-reasons-for-regular-spf-record-checks-in-cybersecurity/dkim-record-check/), performance, and operational efficiency, ensuring that legitimate emails are delivered promptly while minimizing the risk of abuse and disruption. But if you have hit the maximum limit, [get in touch](/contact-us/) with us for help. Also, please feel free to explore our [blog section](/blog/) to educate yourself more on topics related to [SPF](/blog/spf-records-benefits-uses-and-generation/), [DKIM](/blog/when-should-you-rotate-your-dkim-keys/), [DMARC](/10-reasons-for-regular-spf-record-checks-in-cybersecurity/dmarc-record-check/), and phishing. ## Topics [ email security ](/tags/email-security/)[ SPF Flattening ](/tags/spf-flattening/)[ SPF record ](/tags/spf-record/) ![Adam Lundrigan](https://media.mailhop.org/autospf/images/authors/adam-lundrigan.jpg) [ Adam Lundrigan ](/authors/adam-lundrigan/) CTO CTO of DuoCircle. Architect of AutoSPF's SPF flattening engine and DNS monitoring infrastructure. [LinkedIn Profile →](https://www.linkedin.com/in/adamlundrigan/) ## Ready to get started? Try AutoSPF free — no credit card required. [ Book a Demo ](/book-a-demo/) ## Related Articles [ Intermediate 6m 10 Reasons Why DIY-ing SPF isn’t a Good Choice for Companies Apr 4, 2024 ](/blog/10-reasons-diy-ing-spf-isnt-good-choice-for-companies/)[ Intermediate 3m 3 points to consider before setting your SPF record to -all (HardFail) May 22, 2025 ](/blog/3-points-to-consider-before-setting-your-spf-record-hardfail/)[ Intermediate 9m How to clean up your SPF record to avoid email delivery nightmares? Sep 24, 2025 ](/blog/clean-up-spf-record-avoid-email-delivery-problems-guide-tips/)[ Intermediate 6m Decoding SPF mechanisms and their role in maximizing email deliverability Nov 6, 2024 ](/blog/decoding-spf-mechanisms-and-their-role-in-maximizing-email-deliverability/) ```json {"@context":"https://schema.org","@type":"Organization","@id":"https://www.wikidata.org/wiki/Q138897474","name":"AutoSPF","url":"https://autospf.com","logo":{"@type":"ImageObject","url":"https://autospf.com/images/autospf-logo.png"},"description":"Automatic SPF flattening and email authentication management. 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