Why does SPF recursion break email deliverability?

You sent a message. It bounced. Not because the address was wrong—but because your SPF record hit a wall. Not a firewall. A limit. And now your emails aren’t landing, just like that.

SPF records with multiple include mechanisms can trigger recursive DNS lookups that exceed the 10-step limit set by the SPF specification. When that happens, validation fails. No matter how clean your content or how good your sender reputation, the email is rejected before it even reaches the inbox.

This isn’t an edge case. It’s common in organizations using multiple third-party tools—marketing, support, analytics—each adding their own include to your domain’s SPF record. Without a clear picture of the chain, it’s easy to cross the recursion threshold unknowingly.

Key takeaways

  • SPF recursion beyond 10 DNS lookup steps causes validation failure and email delivery breaks.
  • Multiple nested include mechanisms from third-party services are a leading cause of excessive recursion.
  • Even with valid sender authentication, failing SPF due to recursion results in hard bounces and inbox placement drops.

What happens when SPF recursion exceeds the 10-step limit?

When your SPF record includes another record that itself includes another, and so on, you risk exceeding the 10-step recursion limit enforced by major mail providers. Once that limit is hit, receivers like Gmail, Outlook, and Yahoo return a PermError or SoftFail, meaning your email won't deliver. The DNS lookup chain breaks early, and your sender reputation takes a hit.

How recursion triggers permerrors

SPF validation works by recursively resolving included mechanisms. Each include directive triggers a new DNS lookup. If one include points to another include, and that one points to a third, you’re counting steps. Even a single chain of three or four includes can push you over the 10-step threshold used by reputable receivers.

Let’s say your record says v=spf1 include:example.com include:thirdparty.net ~all, and example.com includes another.com, which includes provider.net. If provider.net includes another domain, even if it’s just once, that’s already 10 steps used up. Any further includes break the chain.

This isn’t a theoretical limit—it’s a core part of the SPF specification. The SPF specification explicitly caps recursion at 10 steps. Implementations by major providers like Google and Microsoft enforce this to prevent DNS overload and cache pollution.

Even if one include points to a domain that uses an include, it counts against your total. A single recursive loop—say, A includes B, and B includes A—can cause infinite recursion in theory, though most systems detect and stop it early. But that doesn’t help your delivery.

Why SPF fails when limits are exceeded

When you exceed the limit, the SPF check doesn’t just fail—it fails with a PermError. That means the sender is treated as permanently invalid. Even if your domain is otherwise trusted, your messages may be blocked by receivers that apply strict SPF checks.

Many modern email platforms use SPF as one of three key checks—along with DKIM and DMARC. If SPF fails, the whole message fails validation. No matter how clean your content or how good your sending reputation, a PermError blocks the message before it even enters the inbox.

For example, if you're using a third-party email service that includes your domain in their SPF without proper planning, the inclusion can cause a chain that breaks the 10-step limit. You don’t need a complex setup to trigger this—just one flawed include, or two that point to each other.

Let’s say your domain uses a marketing platform that includes mailservice.com, and they include delivery.net, which includes another.net. If another.net is set up to include your domain, you've just created a loop. This isn’t just theoretical—it’s a common misstep.

That’s why validating your SPF chain before sending is critical. Tools like the MailTester email checker can test how well your domain’s records resolve in real email environments, catching issues like recursion before they harm deliverability.

How to identify excessive recursion in your SPF record

You can identify SPF recursion by tracing the DNS resolution path of your SPF record using tools like MxToolbox or dig. Look for chains of include directives that loop or stack — each one adds a DNS lookup step. If the chain exceeds 10 steps, your SPF record fails validation under RFC 7208, causing authentication issues and deliverability problems. You must break the chain or simplify the logic to avoid failure.

Step-by-step: trace and diagnose recursion

  1. Use a tool like MxToolbox or run dig TXT your-domain.com in your terminal. Focus on the SPF TXT record value, not just the presence of a record. You’ll see the full chain of include: statements.
  2. Trace the path: start with your domain, then follow each include: directive into the next domain’s SPF record. For example, if include:spf1.example.com points to another include, continue until you reach a all or a termination.
  3. Count each include step as one lookup. If you hit 10 or more, SPF validation fails, even if the record syntax is correct. This is a hard limit defined in RFC 7208, the standard governing SPF.
  4. Check for loops. A domain that includes itself, or includes another that includes the first, creates a cycle. Tools like MxToolbox will show infinite loops or repeated domains, which signal an error.
  5. Look for unnecessary include chains. For instance, including multiple vendors’ SPF records in sequence without consolidation often leads to deep nesting. Consider merging or removing intermediaries.

When recursion happens: common causes

  • Multiple third-party services each requiring a separate include directive.
  • Outdated or nested configurations where one include points to another that includes the original.
  • Using generic include patterns like include:spf.protection.com without understanding what’s inside it.

Once you spot a chain with more than 10 steps or a loop, fix the root cause. Remove redundant includes or consolidate them using include only where needed. You can also test changes using the inbox placement tester to verify that deliverability improves after SPF cleanup.

What SPF mechanisms contribute to recursion?

Recursion in SPF records happens primarily when you chain multiple include mechanisms, especially across different vendors or domains. Each include pulls in another SPF record, and if those records include more records, you can hit the DNS lookup limit (usually 10) set by receiving mail servers. The redirect mechanism can also cause recursion if it points to a record that itself includes other records. Using a, mx, or include together increases depth and risk.

Why chained includes are the top culprit

One include is usually safe. But when you have multiple vendors—like your email service provider, marketing platform, and analytics tool—all using include in the same SPF record, you can quickly reach recursion depth. For example, if your primary SPF includes your ESP, which then includes your CRM provider, and that includes your support tool—each additional layer increases the risk of exceeding DNS query limits. This often triggers hard bounces or delivery failures, especially from strict providers like Google and Yahoo.

How other mechanisms amplify risk

The redirect mechanism can cause recursion even if you’re not using include. If it points to another domain’s SPF that has its own includes or redirect, you’re back in risky territory. Combinations like include with a or mx aren’t inherently bad, but they compound depth when layered. For instance, include:spf.example.com with a for a subdomain can add lookup paths, especially if the included record also references other domains.

Sending to thousands of emails? You might not see immediate issues—but as mail volume grows, recipients with high-security filters will start rejecting you. A 2023 study by DMARC Analyzer found that misconfigured SPF records were among the top three reasons for domain reputation loss. You don’t need to know every vendor’s SPF rules—just avoid deep nesting. A clean SPF should stay under 10 DNS lookups, ideally below 5. Use email list verification to test your sending domains and detect weak signals before they hurt deliverability.

Let’s keep things simple: if your SPF uses more than one include, audit it. Replace chained includes with a single, well-maintained record, or better yet, rely on DKIM and DMARC—both of which don’t suffer from recursion. The goal isn’t perfection; it’s reliability.

How to fix SPF recursion without breaking legitimate sender authorization

Chained include statements in SPF records can trigger excessive recursion, leading to DNS lookups that exceed the 10-request limit and cause legitimate mail to fail. To fix this, collapse nested includes into a single, consolidated list of authorized IPs and domains—either manually or via an SPF flattening service. This preserves sender authorization while preventing DNS resolution failures.

Fix SPF recursion with a structured checklist

  • Replace multiple include statements with a single, unified list of authorized domains and IP ranges. This avoids unnecessary DNS lookups and eliminates recursion risk.
  • Use an SPF flattening tool or service to merge all included domains into one cohesive SPF record. These tools parse each include and resolve their IPs before recombining them.
  • Avoid chaining includes across third-party providers. If you must use include, only reference one level deep—never include a domain that itself includes others.
  • If you use include, ensure the final mechanism is ~all or -all only after verifying the total DNS lookup count stays under 10. Use tools like MXToolbox SPF Checker to validate lookup depth.
  • Monitor your SPF record’s DNS lookup count regularly. An SPF record with more than 10 lookups is invalid and will break email delivery.

Validate your fix with real-world testing

After updating your SPF record, test how it behaves in real sender environments. Use inbox placement testing to confirm your messages reach inboxes, not spam folders. A poorly constructed SPF record can cause deliverability issues even if it passes basic syntax checks.

Remember: SPF is not just about syntax—it’s about how systems resolve your record at scale. Overly complex or deeply nested include chains break silently under load. The fix isn’t more complexity; it’s fewer dependencies.

When to use 'all' and why it matters in SPF records

You must include all at the very end of your SPF record to define the default policy—whether mail from your domain passes, fails, or soft-fails. Omitting it makes the record incomplete, and some validators silently treat it as a failure. Placing all earlier in the string can cause unintended policy changes, especially when using modifiers like +all (which allows everything) or -all (which blocks everything), because the order determines evaluation flow.

Why 'all' isn't optional—it’s mandatory

SPF is built on a strict evaluation process. The all mechanism acts as the final decision point. Without it, the rule set stops at the last mechanism, leaving no clear verdict. This leads to inconsistent results: some receivers accept mail, others reject it. According to RFC 7208, the SPF specification explicitly requires a mechanism to cover all possible cases, and all is how you do that.

Let’s say you have v=spf1 include:example.com -all. This works because -all comes after the include. But reverse it to v=spf1 -all include:example.com, and the record fails validation entirely—because the include never gets evaluated. That’s why order matters. Misplacement can cause legitimate mail to be blocked or spoofed messages to slip through, depending on how the receiving server interprets the malformed record.

What happens when 'all' is missing or misplaced

Many organizations accidentally omit all or place it too early—often while trying to "fix" recursion issues. But adding include chains without a final all doesn’t solve the root problem. Instead, it leaves the SPF record in an indeterminate state. This is especially dangerous in complex environments with multiple third-party services. A single missing all can result in high rejection rates across multiple email providers.

Using include without proper end-of-chain handling increases recursion risk, not because the include itself is flawed, but because it creates long, deeply nested evaluations. You're still required to end with all—but it must be the last mechanism. For example, v=spf1 include:mailchimp.com include:sendgrid.net -all is valid. Each include is evaluated, and the final -all defines the outcome.

For a quick check on your SPF record’s structure, use our email checker to verify your domain’s SPF configuration. It highlights common issues like missing all, incorrect syntax, or overlong include chains. If you're building an automated verification system, our SPF validation API can help enforce correct record structure across your senders.

Always treat SPF as a complete, ordered sequence. The all mechanism is not just a formality—it’s the final gatekeeper. Get it wrong, and your messages may not just be rejected—they may be flagged as spam or spoofed.

How MailTester helps validate SPF and detect recursion risk

MailTester’s real-time email verification API catches SPF recursion issues before you send by validating the full DNS chain, including every include directive. It flags excessive nesting or circular includes that could trigger DNS timeouts or rejection, ensuring your SPF records are both compliant and safe. You can test your setup and detect risks instantly, without waiting for bounces or delivery issues.

Checks full DNS chain, not just the surface

When you verify an email address via MailTester’s API, it doesn’t just look at the address itself—it resolves the full SPF record chain, including all include directives. This means if your SPF record relies on multiple third-party providers through nested includes, MailTester traces each one, checking for depth limits or loops. A record that exceeds the 10-DNS lookup limit defined in RFC 7208 will be flagged as a risk.

98.9% accuracy includes catching malformed or recursive records

Our verification process includes validation of SPF syntax and structure. If an include directive points to a malformed or non-existent domain, or creates a loop (like A → B → A), MailTester detects it and surfaces it in the response. This level of detail is built into the 98.9% accuracy rate, which reflects real-world performance across millions of verifications—not just syntax checks, but actual deliverability risk signals.

Let’s say your SendGrid integration uses an include for your domain, which includes another vendor’s SPF, and that one includes back. MailTester sees it and warns you before you send. No guesswork. This isn’t theory—this is the exact kind of issue that can lead to email rejection by receivers like Gmail or Microsoft, as seen in reports from Spamhaus and MXToolbox.

Integrations with SendGrid, Mailchimp, Klaviyo, and HubSpot let you run inbox placement tests and full deliverability checks right in your workflow. Your list gets validated before launch, with recursion risks exposed in real time. Use our real-time verification API to catch issues early, or test inbox placement to see how your message lands across major providers. No expired credits. No wasted sends.

Best practices to prevent SPF recursion in the future

SPF recursion happens when include statements chain too deeply, causing DNS lookups to exceed the 10-query limit. To avoid this, limit includes to one per domain, avoid nesting third-party entries, audit your record regularly using DNS tools, and maintain a single source of truth for approved sending IPs and domains. Let’s break down how.

Keep includes minimal and intentional

  • Use only one include per domain unless absolutely necessary—each adds a DNS lookup, and SPF limits you to 10 total.
  • Never nest includes across multiple vendors (e.g., include:vendor1.com that itself includes include:vendor2.com).
  • If you must include multiple vendors, consolidate them into a single, shared domain that wraps their IPs—this reduces lookup depth.

Audit and validate regularly

  • Run your SPF record through a DNS query tool like MXToolbox monthly to check recursion depth and resolve any issues before they impact deliverability.
  • Use RFC 7208, Section 5.1, as the authoritative guide—SPF lookup limits are standardized and enforced by receiving mail servers.
  • Track all third-party senders in a central list: IP ranges, domains, approved service providers. Update it when onboarding or offboarding a vendor.

When you verify email lists or test send paths, use tools that check both DNS records and SMTP behavior. For example, MailTester’s inbox placement tester simulates real delivery conditions and flags technical issues like SPF recursion early—before you waste sends.

What happens if you don’t fix SPF recursion?

If your SPF record uses include statements that chain too deeply, you risk hitting the SPF lookup limit of 10. When that happens, mail servers return a PermError, causing high bounce rates and blocking your messages before they even reach inboxes. Major providers like Gmail and Outlook will reject your mail or mark it as spam, especially if the error is persistent. This damages sender reputation and lowers domain trust scores, which directly impacts your ability to send transactional or promotional emails reliably.

SPF PermError leads to immediate delivery failure

When SPF recursion exceeds the 10-lookup limit, the receiving server returns a permanent failure — a PermError. This means the email is rejected outright, often without a retry. You'll see increased bounce rates, especially from large providers, which enforce SPF checks strictly. According to RFC 7208, exceeding the limit is explicitly invalid and prevents valid authentication.

Spam filters and reputation suffer long-term

Repeated PermErrors signal poor mail infrastructure to filtering systems. Even if your content is clean, ISPs and filtering services correlate delivery failures with poor sending practices. This harms your sender reputation over time. A degraded reputation reduces inbox placement, especially on platforms like Gmail, Yahoo, and Outlook. As your score drops, messages are more likely to be quarantined, delayed, or outright rejected — even from valid domains.

Major providers use reputation data across multiple dimensions. SPF faults, especially those rooted in misconfiguration, contribute to negative signals. If you're seeing consistent delivery issues or high bounce rates without sending content changes, SPF recursion is a likely root cause. Tools like MailTester’s email checker can help validate your SPF setup against real-world conditions and catch problems before they impact your list.

How to verify your SPF fix is working

You’ve corrected your SPF record to stop recursive includes—now test it properly. Use MxToolbox’s SPF Record Lookup to confirm no recursion occurs. Then, send test emails via MailTester’s inbox placement tool to see if they land in inboxes, not spam. Check bounce reports for “SPF: fail” or “PermError” messages. Monitor delivery metrics over 48–72 hours after changes to catch any lingering issues.

Step-by-step verification

  1. Validate the SPF record syntax using MxToolbox’s SPF Record Lookup. This tool checks for recursive includes, excessive mechanisms, or malformed syntax. It gives you a real-time readout of how the record resolves across DNS. A properly fixed record should show no warnings about recursion, limit the number of include directives, and resolve all mechanisms without exceeding the 10 lookup limit.
  2. Run an inbox placement test with MailTester’s deliverability testing service. Send test emails to known inbox providers (Gmail, Outlook, Yahoo) and verify whether they arrive in the primary inbox, not spam. This shows whether the SPF fix actually improved deliverability. You’ll get a clear report on placement results and any issues detected during delivery. Test real inbox placement across major providers.
  3. Review bounce reports for SPF-specific errors. Look for entries with “SPF: fail” or “PermError” in the envelope or message headers. These indicate a hard failure at the mail server level. Even if the email sends, a "PermError" means the record is invalid and won't pass checks. This helps you distinguish between delivery blockage due to SPF vs. other issues like DNS or blacklists.
  4. Monitor bounce rate and inbox placement over 48–72 hours. SPF changes don’t take effect immediately. Delayed propagation and temporary DNS caching can mask failures. Track delivery success over time. A stable bounce rate under 0.5% and consistent inbox placement mean the fix has taken hold. Use tools like MailTester’s bulk verification or API to audit sender reputation and detect anomalies early.

Why timing and logs matter

SPF validation happens at the MTA level, not the user’s client. A successful delivery on your end doesn’t mean the recipient’s mail server accepted it. The only way to know for sure is to simulate real delivery. Use MailTester’s API for real-time validation of individual addresses, especially when validating large lists.

When dealing with complex records, refer to RFC 7208 for the official specification of SPF syntax and limitations. The standard defines a hard limit of 10 DNS lookups per SPF check—exceeding it results in a PermError, which breaks delivery.

Conclusion: Fix recursion now, avoid delivery failure later

SPF recursion isn't a minor configuration quirk—it’s a direct cause of email rejection. Each recursive include deepens the evaluation path, triggering hard failures at the receiving end.

The fix is measurable and repeatable

  • Audit your SPF records for nested include chains using tools like MxToolbox or DNS lookup utilities.
  • Reduce the depth to three or fewer includes to stay within RFC limits.
  • Validate with a real-time SPF tester before deploying changes at scale.

Even small fixes in SPF configuration have a meaningful impact on inbox placement. Delaying resolution means risking delivery to 10–20% of domains that enforce strict SPF policies.

Sources

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Frequently asked questions

What is SPF recursion?

SPF recursion occurs when one SPF record includes another, which itself includes a third, exceeding the 10-DNS-step limit. This breaks SPF validation.

How many include statements are too many in SPF?

More than 10 include steps total across the chain break SPF. Even 3–4 nested includes can exceed the limit if not managed.

Can I use include with multiple vendors?

Yes, but only if each include is shallow. Prefer combining them into a single list rather than chaining them.

What is the 10-step limit in SPF?

SPF DNS lookup depth must not exceed 10 mechanisms (including includes, redirects). Exceeding this causes validation failure.

Do all email providers enforce SPF recursion limits?

Yes. Major providers like Gmail, Outlook, and Yahoo enforce the 10-step limit to prevent abuse and DNS overload.

How do I test my SPF record for recursion?

Use tools like MxToolbox or Dig to trace the DNS resolution path. Look for chains longer than 10 steps.

Can I use include:spf01.example.com safely?

Yes, if the included domain doesn’t point to another include. Each 'include' counts as one step in the chain.

How often should I audit my SPF record?

Audit at least monthly, especially when adding new email services or changing senders.

Does MailTester check SPF recursion?

Yes. MailTester’s real-time verification API and inbox-placement tests detect SPF depth issues and invalid records.

What happens if SPF fails on a send?

The email may be rejected with a 'PermError' or delivered with a 'SoftFail'—both harm deliverability and reputation.

Can I use both SPF and DMARC if SPF is broken?

Yes, but DMARC enforcement will fail without a valid SPF result. Always fix SPF before enabling strict DMARC policies.

Is there a tool to flatten SPF records automatically?

Yes—some security and email platforms offer SPF flattening. You can also manually compile all allowed IPs into one record.