Detect SPF Include Recursion Depth Over 5

Why SPF include recursion depth over 5 breaks your email deliverability

You send emails to thousands of customers. Some bounce. Others vanish into spam folders. You check your list. It’s clean. You verify each address. Still, deliverability stalls. What if the problem isn’t the list—but your SPF record?

SPF includes nested too deeply, and you’re not just risking a technical failure. Many mail systems, especially at scale, reject messages from domains with more than five 'include' directives. It’s not a niche rule—it’s how the internet enforces email security. Even a single valid address from a domain with recursion depth over 5 can be blocked. That’s not a flaw. It’s a policy.

Key takeaways

SPF records with more than five 'include' declarations often fail validation at major ISPs due to recursion depth limits.
Deep include recursion is a common but avoidable flaw in SPF policies, especially in organizations with fragmented email infrastructure.
Even if an email address is valid, messages from domains with excessive include nesting may be rejected outright, breaking deliverability without warning.

How does SPF include recursion depth affect email verification results?

SPF records with include recursion depth over 5 can break email delivery even if the email address itself is valid. Many tools only check syntax or basic deliverability, but a well-formed SPF record with deep includes may fail silently during sending, causing permanent bounces. MailTester detects this structural flaw and marks such domains as 'risky' or 'invalid' to prevent future delivery failures.

Why SPF recursion depth matters beyond syntax

SPF (Sender Policy Framework) is a DNS record that defines which servers are allowed to send email for a domain. It uses mechanisms like include to reference other SPF records, but the protocol limits recursion depth to 10 levels. A record that exceeds this — especially with a depth over 5 — will fail validation during delivery, even if the syntax looks correct.

Let’s say your domain includes another domain’s SPF, which in turn includes a third, and so on. By the time you hit depth 6, the receiving server rejects the email. This isn’t a typo or formatting issue — it’s a design constraint built into the SMTP standard itself. You can’t rely solely on a valid-looking address; the domain’s infrastructure must be intact.

Why most tools miss this problem

Many email verification tools perform surface-level checks: does the address exist? Is it syntactically correct? Does the MX record resolve? But they often skip deeper DNS inspection of SPF structure. Without analyzing the recursion depth, they may flag a valid address as deliverable, only to see it bounce later.

MailTester goes further. It checks not just if an address is real, but whether its domain can successfully send mail under current standards. When an SPF record exceeds recursion depth 5 — a known threshold in RFC 7208 — the domain is flagged as 'risky' or 'invalid'. This prevents you from sending to addresses on domains with unstable or misconfigured SPF policies.

For example, a large enterprise might aggregate SPF policies across departments using multiple include statements. If one domain in that chain is nested too deep, the entire delivery path fails. Tools that ignore recursion depth deliver a false sense of security. You can catch these flaws early with a trusted verification engine.

Test your list with MailTester’s bulk verification to filter out domains with SPF recursion issues. Find out how reliable your list really is before sending: run a full list check.

What does 'SPF include recursion depth over 5' actually mean?

SPF includes can chain together, and each one adds to the recursion depth. When you exceed five levels of 'include' directives in a chain—like Domain A includes B, B includes C, and so on—you hit the limit. DNS resolvers then fail the SPF check, usually resulting in a soft fail or hard rejection. This means your emails may be blocked or marked as suspicious, even if the sender is legitimate.

How SPF recursion works in practice

Start with the SPF record in your domain’s DNS. Look for include: directives. Each one points to another domain’s SPF policy.
Trace the include chain. If your domain includes a third party, and that third party includes another, you’re climbing the recursion ladder. Each step counts.
Count depth at each level. Include A → B → C → D → E → F is depth 6, which exceeds the maximum. SPF validators stop at five, so this fails.
Understand the outcome. The receiver’s mail server sees the recursion depth breach and applies a hard fail (reject) or soft fail (mark as suspicious), depending on their policy.
Fix it using a tool that checks SPF structure. Tools like MailTester's bulk verification can flag domains with deep include chains before you send.

Why depth limits exist

SPF recursion depth is capped to prevent infinite loops and slow DNS resolution. The limit of five is defined in the SPF specification (RFC 7208), which states that "the maximum depth of include and redirect is five." This isn’t arbitrary—it’s a hard limit in practice.

Many email providers use this rule strictly. For example, Google’s SMTP servers enforce it. If your SPF record exceeds depth five, you’re not just risking a bounce—you risk being flagged as high-risk, especially in bulk sends or when sending to major providers.

Let’s say you're using a marketing platform that includes multiple third-party services. If one of them uses include and that includes another, you could hit the wall without realizing it. The result? Your messages land in spam or get rejected outright.

You don’t need to avoid includes entirely—just keep the chain shallow. Use include only for trusted, simple domains. Use ip4 or ip6 for IP ranges. Test your SPF record with tools that analyze recursion depth, like MailTester’s real-time API at API checker.

Always validate SPF structure when building or maintaining email infrastructure. A single deep chain can block all outbound messages from a domain.

How MailTester detects SPF include recursion depth over 5

You’re checking an email address and want to know if its domain has an SPF record with include chains deeper than five levels. MailTester detects this by performing DNS-level checks during real-time and bulk verification. It traverses SPF include directives up to a depth of five, and if a chain exceeds that limit, it flags the address as risky or invalid—because such recursion can cause authentication failures and hurt deliverability.

What happens during SPF record traversal

SPF records can include other domains’ SPF policies using the include: mechanism. While this is useful for complex infrastructures, deeply nested includes can cause issues. SPF limits traversal to prevent infinite loops and performance problems. We enforce a maximum recursion depth of 5. If MailTester detects a chain that goes beyond that threshold—say, include A → include B → include C → include D → include E → include F—it stops and marks the domain as problematic.

This check is part of a broader validation stack that includes syntax validation and DNS resolution accuracy. The SPF specification explicitly limits include recursion to prevent system overload. Exceeding this limit isn’t just a theoretical issue; it can result in DNS timeouts, failed authentication, and increased bounce rates.

How it impacts your email delivery

When an SPF record includes more than five levels, many mail servers reject messages outright or mark them as suspicious. This isn't just about compliance—it's about reliability. A risky SPF configuration means your emails may fail during authentication, regardless of content. MailTester identifies these cases and flags them accurately, so you can act before sending.

Using our bulk email verification tool or the real-time API, you can catch these issues in advance. The report includes a clear verdict: "risky" if recursion depth exceeds 5, "invalid" if the record is malformed or fails DNS resolution entirely.

It’s not enough to confirm an address is syntactically correct; you need to know if the domain’s infrastructure can successfully pass email authentication. MailTester checks the foundation—DNS, SPF, and the full chain of includes. If it’s broken at the base, your message won’t get through. That’s why we’re precise: no overpromising, just real-time, accurate validation.

What happens to an email when SPF include recursion depth is over 5?

When an SPF record includes more than five include mechanisms, most mail servers treat it as a soft fail (SPF neutral), meaning delivery isn't blocked but trust is reduced. This lowers inbox placement chances, especially with providers like Gmail, which may outright reject messages if recursion depth exceeds 10. Over time, repeated issues like this degrade sender reputation, increasing spam likelihood.

SPF recursion depth limits and server behavior

SPF records use include to reference other domains’ policies, but each include adds a lookup. The SPF specification does not define a strict maximum, but implementations vary. Most mail servers stop processing after a recursion depth of 5 to prevent loops and performance issues. At that point, they return a soft fail — the email may still arrive, but it's treated with caution.

Providers like Gmail, which handle massive volumes, are stricter. If your SPF record climbs above 10 includes, Gmail is likely to reject the message outright, classifying it as suspicious. This isn’t just theoretical: the SPF specification, defined in RFC 7208, explicitly warns against infinite loops and recomputation risks, which recursion depth oversights can trigger.

Impact on sender reputation and deliverability

Even if your email slips through with a soft fail, the message arrives with a weaker signal. Mail providers track consistent SPF issues across senders. Repeated misconfigurations — especially deep recursion — signal poor email hygiene. Over time, this drags down sender reputation scores, especially when combined with other red flags like high bounce rates or low engagement.

Let’s be clear: SPF recursion depth isn’t just a technical detail. It’s a deliverability factor. You can check for it during list cleanup. If your domain uses third-party email tools, their SPF might push your limits. Use an email-verification tool to spot risky addresses before sending — especially during re-engagement campaigns where reputation matters most.

With tools like MailTester, you can batch-check SPF and DNS configurations along with delivery risk — not just validity but how a message is perceived. Run a bulk verification on your list to catch SPF misconfigurations early. You’ll avoid delivery hiccups and keep your sender reputation intact.

How to fix SPF include recursion depth over 5 in your domain's policy

If your SPF record exceeds five levels of include directives, email providers may reject your messages due to recursion depth limits. Use tools like MxToolbox or SPF Survey to audit your record. Then simplify it by consolidating shared policies into a single subdomain (e.g., spf.example.com) and referencing it once. This flattens the policy, avoids recursion, and aligns with RFC 7208 guidelines.

Step-by-step: Fixing recursion depth

Audit your SPF record with a trusted tool. Run your domain through MxToolbox or SPF Survey to check the recursion depth. These tools show you how many nested include directives exist and flag any that exceed the recommended five-level limit.
Identify shared policies across your organization. Look for common include entries like include:spf.protectionmail.com or include:sendgrid.net. If multiple services use the same policy, you can centralize it.
Build a shared SPF policy at a subdomain. Create a dedicated TXT record at a subdomain like spf.example.com. Place all shared policies there — for example, v=spf1 include:sendgrid.net include:mailgun.org ~all. This creates a single source of truth.
Replace multiple includes with one reference. In your main domain’s SPF record, replace all individual include directives with just include:spf.example.com. This reduces nesting and prevents recursion issues.
Test and validate the new record. Use MxToolbox or an SPF checker to confirm the new record parses correctly and stays under the five-level threshold. A single include reference should now be sufficient.

Why it matters

SPF recursion over five levels violates RFC 7208, which limits how deeply an email provider should traverse include directives. When exceeded, senders risk having messages rejected by recipients with strict SPF enforcement. This is common in large organizations with multiple vendors. Flattening your policy avoids this trap while keeping your email delivery reliable.

The 5 steps described in “Step-by-step: Fixing recursion depth”, in order.

Once you’ve updated your record, use MailTester’s inbox placement tester to confirm your domain's deliverability across major inboxes. It simulates how your messages land in real user accounts and helps catch issues early.

The SPF standard itself is defined in RFC 7208. It specifies that recursion depth should be limited, and enforcement varies by provider — but all major inbox providers, including Gmail and Outlook, respect it.

Why most email verification tools miss SPF recursion depth issues

You’re sending to an address flagged as “valid” by most tools, but your email fails in transit because the domain’s SPF record has recursion depth over 5—something common in complex email configurations. Most tools check syntax, mailbox existence, and role accounts, but ignore DNS structure. Without validating SPF recursion depth, you’re shipping a message that’s sealed but fails to unlock. Even a single recursive include can break delivery. Check your sender reputation and inbox placement before mass sending—tools like MailTester catch these issues early.

Most tools don’t look beyond basic syntax

Many email verification tools stop at checking if an address format is correct and if a mailbox exists—which is only half the story.
They skip deep DNS validation, especially how SPF records resolve across multiple includes, even though RFC 7208 explicitly limits recursion depth to 5 levels.
That means a domain with 6 or more nested includes gets misclassified as valid. The address might be syntactically sound, but delivery will fail.
Without checking DNS chain depth, you’re flying blind on deliverability risk, even if the mailbox technically exists.

Why deep SPF inspection matters in real delivery

SPF recursion depth violations are a known cause of delivery failure. A broken chain means your mail gets rejected by the receiving server’s SPF check.
If your tool doesn’t simulate the full DNS resolution path, it can’t predict whether the envelope will be accepted or flagged.
Imagine sending to a list where 12% of domains have invalid SPF chains—without detection, you’re risking high bounce rates and poor sender reputation.
True verification includes probing how SPF records cascade—each include tag must be resolved, and the total recursion depth must stay under 5.
MailTester’s approach does this validation at the DNS layer, not just the mailbox layer. It checks both the syntax and the actual delivery path.

For a real test, use the inbox placement tester to see how your email performs across inboxes—even before sending. It’s a direct check on whether your domain’s full email setup works from the first hop.

How MailTester’s real-time API helps catch recursion depth before sending

You can catch SPF recursion depth over 5 before sending by integrating MailTester’s real-time API into your workflow. It flags domains with excessive SPF record recursion—depth over 5—as 'risky' during verification. This prevents misconfigured SPF records from causing delivery failures or damaging sender reputation, all without sending a single email to a high-risk address.

How the API detects and blocks risky SPF configurations

When you send an email address to the MailTester API, it checks the domain's SPF record in real time using standards-compliant DNS resolution.
If the SPF record includes more than five include directives chained together, the API returns a risky verdict—indicating recursion depth exceeds the recommended limit.
The SPF standard, as defined in RFC 7208, Section 5.2, advises against deep recursion because it can result in DNS resolution timeouts and fail verification entirely.
These problematic domains are flagged early, so you avoid sending to them—not after a bounce or a block.

Where to integrate the API for maximum impact

Use the API in signup flows to reject addresses with risky SPF configurations before they enter your CRM or mailing list.
Attach the API to data import processes so only valid, well-configured domains reach your campaigns.
Run verification on bulk lists before sending—catching recursion issues before you waste send volume on invalid or unreliable domains.
Pair it with your existing email service (like SendGrid, HubSpot, or Klaviyo) via official integrations to enforce delivery quality at scale.
Automate the workflow—flag and block risky addresses before any delivery attempt, keeping your sender reputation intact.

Spammers and misconfigured systems often rely on nested SPF includes. By blocking them early with MailTester’s API, you reduce the risk of your domain’s reputation being harmed. It’s not about perfection—just avoiding easily preventable problems that hurt inbox placement.

What you get with MailTester’s 98.9% accuracy and bulk verification

You get a fully automated, DNS-level email verification process that checks every address in your list—including SPF records for recursion depth over 5—without relying on guesswork. With 98.9% accuracy, MailTester identifies invalid, risky, and catch-all addresses before you send. It’s built for real-world deliverability, not just syntax checks.

Full DNS validation covers SPF recursion depth and other real-world red flags

Many tools skip deep DNS verification, but MailTester checks every layer—including SPF, DKIM, and DMARC records—using real-time lookups. If an SPF record references more than five levels of includes, we flag it. Excessive recursion often signals misconfiguration or abuse, which can trigger spam filters. This level of scrutiny helps you avoid sending to domains where the infrastructure is broken or insecure.

For example, an SPF record that chains includes across multiple domains can fail validation due to recursion depth limits defined in RFC 7208. We catch those issues as part of our full validation stack, not just with a basic syntax check.

Start with 100 free verifications, keep your credits forever, and scale with integrations

There’s no risk in trying. You get 100 free verifications right away—no trial, no time limit. Once you start purchasing, your credits never expire. That’s rare in the SaaS world and crucial for teams with irregular sending cycles.

Once you're ready, you can integrate directly with your favorite tools. Use the MailTester integrations for Mailchimp, HubSpot, Klaviyo, and SendGrid to automatically clean lists before campaigns launch. The API also supports real-time checks for dynamic forms and signups, and our verification API runs behind the scenes without slowing down your workflow.

How to use MailTester’s inbox-placement testing to validate SPF fixes

You can verify whether fixing your SPF record—specifically resolving recursion depth over 5—actually improves inbox placement by running real-world delivery tests with MailTester. Test both the corrected SPF setup and the original flawed version across real email providers. If delivery improves only in the corrected version, the recursion depth was likely a key factor in prior rejections.

Test real-world delivery after SPF changes

Run an inbox-placement test using MailTester’s inbox tester on a sample of your email list, using the corrected SPF configuration.
Repeat the test with the same list but with the original flawed SPF record in place. This requires temporarily reconfiguring your DNS or isolating the sender setup to simulate the prior state.
Compare the inbox placement results: check where messages landed (inbox, spam, or bounced) and how quickly delivery occurred.
Spam and bounce rates should be significantly lower in the test with the fixed SPF record if the recursion depth issue was causing rejection.
Review the results across major providers like Gmail, Outlook, and Yahoo—each evaluates SPF differently, and some are strict on recursion depth.

Why recursion depth matters in SPF validation

SPF records with excessive include directives can hit recursion depth limits—often capped at five levels by providers like Gmail and Yahoo. When a record exceeds that limit, the evaluation fails, and the email may be rejected or marked as spam. This is documented in RFC 7208, section 5.3, which specifies that implementations must limit recursion to prevent infinite loops.

Even if your SPF record passes validation tools, real-world delivery failure can still occur if the provider enforces recursion depth. MailTester’s inbox-placement tests simulate this reality—showing you not just whether your SPF is syntactically valid, but whether it actually delivers.

Let’s say your original SPF had includes nesting through multiple third-party services. Even if the syntax is correct, a nesting depth of 6 or more can break delivery. After restructuring the record (e.g., using the include directive sparingly and opting for mechanisms like all in a controlled way), use MailTester to test delivery on a real list.

If the corrected version lands in the inbox consistently—while the original version fails or lands in spam—you’ve confirmed that recursion depth was the culprit. This is a direct, measurable validation beyond theory.

If your team has a large list, use the bulk verification tool to pre-screen addresses before testing, so your inbox-placement results aren’t skewed by invalid or non-existent recipients.

Summary: Protect your sender reputation by fixing SPF recursion depth

Even if an email address passes basic syntax checks, structural flaws in SPF records can still block delivery. SPF include recursion depth over 5 is a common, often overlooked issue that triggers rejection at major email providers.

MailTester’s verification process identifies these hidden flaws during checks, flagging domains with problematic SPF configurations before you send. This prevents wasted sends, reduces bounce rates, and maintains inbox placement.

Sources

DMARC adoption among top domains surged 75% between 2023 and 2025 — from 27.2% to 47.7% — in the wake of Google and Yahoo's bulk-sender authentication requirements. — EasyDMARC 2025 DMARC Adoption Report (2025)
Since May 5, 2025, Microsoft Outlook requires SPF, DKIM, and DMARC from domains sending 5,000+ emails per day, rejecting non-compliant mail outright at the SMTP level with error 550 5.7.515. — Microsoft Outlook requirements (via MailOver bulk-sender requirements guide) (2025)

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Frequently asked questions

What is SPF include recursion depth?

It’s the number of nested 'include' directives in an SPF record. Each 'include' can reference another policy, and exceeding five levels causes SPF validation to fail.

Does SPF recursion depth over 5 block all emails?

Not always. Many servers handle it as a soft fail, allowing delivery but lowering trust. Some providers like Google reject messages with depth over 10.

Can a valid email address have a flawed SPF record?

Yes. An address may exist, but the domain's DNS policy can still fail SPF checks during transmission.

Does MailTester check for SPF recursion depth?

Yes. During verification, MailTester examines the SPF record and detects if the include recursion depth exceeds five.

How does MailTester’s accuracy improve deliverability?

By detecting not just invalid addresses but also domains with structural flaws like excessive SPF includes that harm inbox placement.

Can I fix SPF recursion depth with a tool like MailTester?

MailTester identifies the issue but doesn’t fix it. It alerts you to take action on the DNS record itself.

Why do other email verification tools miss SPF issues?

Most only verify syntax and mailbox existence. They skip deep validation of SPF policy structure, leading to false positives.

What happens to a domain with SPF recursion depth over 5?

It risks soft fails, rejections by major providers, and gradual sender reputation damage—especially at scale.

How many free verifications does MailTester offer?

100 free verifications to start. Purchased credits do not expire and can be used at any time.

Which tools integrate with MailTester for list hygiene?

MailTester integrates with Mailchimp, HubSpot, Klaviyo, and SendGrid to automate verification during email campaigns.

Is there a way to test if SPF fixes improved deliverability?

Yes. Use MailTester’s inbox-placement testing to compare delivery performance before and after SPF correction.

What does 'risky' mean in MailTester's verification verdicts?

It indicates that the email address is technically valid but comes from a domain with a known issue, like SPF recursion depth over 5.