Optimize SPF Records to Avoid Expansion Issues

Why is SPF include mechanism expansion a real problem for deliverability?

You’ve set up SPF for your email service, added a few includes for your third-party tools, and everything seemed to work. Then one day, your deliverability starts slipping — some emails bounce hard, others land in junk folders. No clear reason. The issue might be hiding in plain sight: SPF include mechanism expansion.

When your SPF record chains too many include: directives, DNS lookups pile up. RFC 7208 caps this at 10 lookups. Exceed that, and the validation fails. No graceful warning. Just a hard fail. And that breaks deliverability the moment a receiving server checks your SPF.

Every include adds a new lookup. A single tool might pull in two or three records. Combine that with your own includes, your ESP’s, and your marketing platform’s — and you’ve hit the limit before you realize it. SPF isn’t just about listing senders. It’s about keeping the chain of trust under control.

Key takeaways

SPF record expansion fails when DNS lookup depth exceeds the RFC 7208 limit of 10.
Multiple include: directives from third-party services can cumulatively trigger expansion failures.
SPF validation failure results in hard bounces and degraded sender reputation, even if the email is legitimate.

What happens when SPF include mechanisms expand beyond the 10 DNS lookup limit?

When your SPF record uses too many include directives, each one triggers a DNS lookup—even for a simple TXT record. Once you hit 10 lookups, the receiving mail server returns a permerror, a permanent failure that blocks your emails from landing in inboxes, not just spam folders. This isn’t a soft fail or a warning—it’s a hard rejection.

How include directives consume DNS lookups

Every time your SPF record references include:example.com, the receiving server makes a DNS query for that domain's SPF record. Even if the record exists in cache, it still counts toward the limit. You’re not limited to your own SPF record—the include chain can pull in multiple external domains, each adding one lookup.

For example, if you use include:sendgrid.net and include:mailchimp.com, and each of those includes another domain, the chain can grow fast. That’s why even a few includes can push you over the 10-lookup threshold, especially when third-party services chain their own includes.

Why permerror is a hard stop for deliverability

A permerror means the SPF policy failed permanently, not temporarily. Unlike softfail or neutral, which allow email to pass, a permerror often triggers immediate rejection. Receiving servers treat this as a sign of misconfiguration or abuse.

This is why RFC 7208 (the standard for SPF) explicitly limits DNS lookups to 10. It’s not a suggestion—it’s a requirement. You can’t exceed it without risking delivery. The limit exists to prevent performance issues and spoofing via long chains.

Check your SPF record with a tool that shows lookup depth. Tools like MXToolbox or DMARC Analyzer can simulate real-world validation and show where you’re hitting limits.

Let’s be clear: every include, even for a provider you trust, counts. Redundant or overlapping includes compound the problem. The best fix isn’t to remove all includes—it’s to trim what you don’t need and use ip4 or ip6 when possible.

Test your SPF record regularly. Use MailTester’s inbox placement test to see how real providers evaluate your setup. You’re not just checking syntax—you’re simulating real delivery decisions that impact engagement and reputation.

How to audit your current SPF record for include expansion risk?

You can audit your SPF record by tracing every include directive using a DNS lookup tool like MxToolbox or dig. Each DNS resolution—whether from include, redirect, a, mx, or exists—counts toward the 10 lookup limit. If you have more than five nested includes, expansion risk increases significantly.

Step-by-step audit process

Retrieve your current SPF record from your domain’s DNS zone. Use dig txt yourdomain.com or check via MxToolbox’s SPF checker to confirm it’s properly published.
Isolate each include directive. These are entries like include:_spf.google.com or include:spf.example.net. Note every one.
Resolve each include manually using a tool like MxToolbox or dig. For each, follow the chain: does the included domain have its own SPF? Does that one include another? Trace the full path.
Count every DNS lookup in the chain. Each include, redirect, a, mx, or exists consumes one of the 10 allowed lookups. A single include may trigger multiple resolves.
Check for deep nesting. If any path branches more than five levels deep (e.g., A → B → C → D → E → F), you’re approaching or exceeding the limit—and spammers exploit this to cause failures.

Why this matters

SPF was designed to be a lightweight header, but overuse of includes causes excessive DNS queries. The Internet Engineering Task Force (IETF) limits lookups to 10 per validation (see RFC 7208). When a record exceeds this, the result is a temporary failure—a “soft fail”—which harms sender reputation and inbox placement.

The 5 steps described in “Step-by-step audit process”, in order.

Even if your record technically passes validation, repeated failures due to expansion risk reduce sender trust with receiving mail systems. This is why services like inbox-placement testing are crucial—proactively identifying issues before they hit customer inboxes.

“A well-managed SPF record avoids nested includes. It's better to use a single, authoritative source with updated mechanisms than to rely on deep chains.”

As an alternative, consider using include only for trusted, stable domains. For dynamic services, evaluate if a spf2.0 mechanism or a centralized record (e.g., via a third-party provider’s shared domain) reduces complexity. Tools like MailTester’s bulk verification help validate sender configuration at scale by catching issues before sending to real users.

If you’re using our API, it can help assess email validity—and indirectly highlight sender-side configuration risks, including those caused by SPF mismanagement. Keep records lean. When in doubt, measure the depth of includes in your chain.

What are the most common SPF include expansions that cause issues?

SPF include expansions fail most often when you stack multiple third-party providers, include domains that themselves use 'include' directives (causing recursion), or rely on outdated syntax like 'v=spf1' without closing mechanisms like 'all' or 'exp'. These patterns push SPF lookups past the 10 DNS resolver limit, triggering permanent fails and spam flags.

Overloading SPF with multiple third-party providers

You're likely running into expansion issues if you've added SendGrid, Mailchimp, HubSpot, and a dozen other services using separate 'include' directives. Each 'include' adds a DNS lookup. When these stack—especially across nested or redundant inclusions—your SPF record quickly hits the 10-lookup limit defined in RFC 7208. The result? A hard fail, even if your email is legitimate.

It’s not just volume—misaligned providers can also conflict. For example, some services expect 'allow' rather than 'redirect', and improper stacking breaks alignment. If you’re using a tool like MailTester’s integrations with HubSpot or SendGrid, ensure your SPF record is streamlined and avoids redundant includes.

Recursive delegation with include chains

Problems escalate when you include a domain that already uses 'include'—like including a provider whose own record includes another service. That creates chains: include:spf.example.com, which might include include:thirdparty.com, which then includes include:cloudmail.com. Each step counts toward the 10-lookup limit, and once you exceed it, SPF validation fails.

This recursive use of 'include' is a common oversight. The SPF design doesn’t support it—only one level of inclusion is intended per domain. If you’re unsure whether a domain’s SPF is safe to include, check its full record via tools like MXToolbox or test it in real time with MailTester’s inbox placement features.

Legacy syntax without proper closure

Using old 'v=spf1' formats without explicit 'all' or 'exp' mechanisms makes records vulnerable to expansion failures and misinterpretation. Without 'all', SPF has no defined policy. Without 'exp', you miss fallback messaging for diagnostic clarity.

Let’s be clear: SPF syntax isn’t just about listing services. It’s about policy closure. Always end your records with all or use exp to define error response behavior. A malformed or incomplete record can cause delivery issues even if your authentication appears correct. For a real-world check, use MailTester’s bulk verification to test your domain’s SPF consistency across sender lists.

How to reduce SPF include depth without sacrificing authentication coverage?

You can reduce SPF include depth by limiting includes to only essential, provider-specific records with low lookup costs, avoiding nested includes from unrelated domains, and consolidating multiple senders under a single, centralized SPF record—especially one from your primary email service provider. This minimizes expansion risks while maintaining full authentication coverage.

Limit includes to provider-backed, low-lookup records

Use only include directives from email service providers that offer a single, unified SPF record with minimal DNS lookups—like include:_spf.google.com or include:spf.protection.outlook.com.
Avoid chaining multiple include statements from different vendors, especially if they each trigger their own DNS query, as this increases expansion depth and the risk of failure.

Prefer centralized SPF ownership over fragmented includes

Instead of including multiple senders’ SPF records, designate one primary sender (e.g. your ESP) with a full, comprehensive SPF record and only include their service—even if you use several tools, centralize the SPF at the main provider.
Only include domains that actively send email on your behalf; skip those that are passive (e.g., analytics platforms, third-party tracking tools) or don’t send messages.
When adding includes, always check the resulting DNS lookup count—any SPF record with more than 10 lookups fails due to RFC 7208 limits.
Monitor DNS results with tools like MXToolbox or RFC 7208 to ensure your SPF is within safe lookup limits and avoid the "include recursion" trap.
Use a dedicated email-verification service like MailTester’s bulk verification to identify invalid or malformed email addresses before sending, reducing the load on your SPF and preventing unauthorized senders from slipping in.

When in doubt, consolidate. One well-structured SPF record from your primary sending provider is more reliable than a deep, scattered chain of includes.

If you rely on multiple third-party services, consider using DMARC with SPF alignment and monitoring—this lets you enforce policy while tolerating some include depth, but only if you're tracking alignment failures.
Set up regular SPF audits using DNS tools or your ESP’s reporting, and disable includes from domains that no longer send on your behalf.

When to consider using SPF alignment with DMARC for stronger security without expansion?

You can reduce dependency on complex SPF includes by aligning your SPF records with DMARC policies. When DMARC enforces alignment, only messages where the From domain matches the domain in the SPF authentication result are considered valid. This allows you to simplify SPF (e.g., dropping include: chains) while still protecting sender identity and improving inbox placement — without hitting SPF’s 10 include limit.

How SPF alignment reduces expansion risk

SPF’s include: mechanism can expand into long chains of DNS lookups, which often exceed the 10-lookup limit and cause hard failures. By relying on DMARC alignment instead, you avoid building expansive SPF records altogether. The From domain only needs to match the domain used in SPF’s authentication step — not necessarily the full chain.

For example, if you send from [email protected] and authenticate via spf=pass (sender=yourcompany.com), DMARC alignment checks whether the From domain matches. If yes, the message passes even if SPF doesn’t include a long list of third-party providers.

DMARC policy alignment improves deliverability

A moderate DMARC policy — like p=quarantine or p=reject — gives senders a path to improve inbox placement while minimizing false positives. Starting with p=none lets you monitor alignment without affecting delivery. You can then move to p=quarantine to flag non-aligned messages in DMARC reports, and eventually p=reject to block them.

This approach works well even with simpler SPF records. It’s not about replacing SPF, but about reducing over-reliance on complex includes — which is why industry guidelines from RFC 7489 emphasize alignment as a core component of email authentication.

Let’s be clear: you still need to validate your domains and email workflows. Use tools like the inbox placement tester to simulate how your messages land across major inboxes. It’s one way to validate that your DMARC alignment strategy is working in practice.

Can SPF records use 'redirect' instead of 'include' to reduce lookup load?

You can use redirect instead of include in SPF records to avoid expanding lookup chains, but it doesn’t eliminate DNS load — the target record still triggers lookups. Only use redirect if the target domain is explicitly designed for delegation, and be cautious: indirect chains can still lead to expansion, especially if multiple levels are involved.

How 'redirect' works and when it applies

The redirect mechanism completely replaces your SPF record with the one from the specified domain. If you set redirect=trusted-sender.net, for example, the entire SPF policy of trusted-sender.net applies to your domain. This avoids stacking multiple include directives, which can cause lookup overflows.

But here’s the catch: the target domain (e.g., trusted-sender.net) still requires a DNS query. If that domain itself includes other sources or uses redirect, the lookup chain continues. So while redirect can simplify your record, it doesn’t remove risk — just shifts it.

When 'redirect' can cause unexpected expansion

Imagine you redirect to a trusted third party, but that domain includes another domain with its own include. Now you’re back to the original problem: nested lookups. DNS resolution can hit the SPF limit of 10 lookups, which can trigger SPF failures even if your setup seems clean.

Use redirect only when you fully control the target domain or have been explicitly granted delegation rights. Relying on third parties with complex SPF chains introduces risk. According to the SPF specification (RFC 7208), redirect is intended for trusted, well-managed domains, not for general inclusion of unverified or loosely maintained sources.

Let’s be honest: SPF optimization isn't just about eliminating lookups. It’s about reducing complexity while maintaining trust. For teams sending at scale, testing each record’s impact is essential. Tools like MailTester’s inbox placement can help detect issues before they cause bounces or blocklists. Run your SPF strategy through real-world tests with actual email clients.

And remember: if you’re validating lists or checking domain health, you're already ahead of the curve. Using bulk verification can expose invalid or misconfigured domains before they affect your sending reputation. A single misaligned SPF record can impact deliverability — fix the root cause, not just the symptom.

How to validate SPF record compliance before sending mail?

Verify your SPF record's syntax and lookup limits using a real DNS analyzer, then simulate a full evaluation to catch include mechanism expansion issues. After confirmation, test delivered messages with an email verification service like MailTester to ensure real-world success across inbox placement, SPF validation, and sender reputation.

Step-by-step SPF validation process

Run your SPF record through a DNS analyzer like MxToolbox's SPF lookup tool. This checks for common syntax errors, such as duplicate mechanisms, invalid qualifiers, or missing closing quotes. It also helps you spot problematic includes that could trigger expansion limits during email delivery.
Verify lookup count limitations using a full evaluation simulator. SPF has a 10 DNS lookup limit per email. Each include, redirect, or exists mechanism counts toward this. Tools that mimic real mail server behavior will warn you if your record exceeds this threshold during evaluation.
Use an email verification service like MailTester to test deliverability from real endpoints. After confirming your SPF record is syntactically correct and under the lookup limit, send a test message through your actual sending infrastructure. MailTester’s inbox placement test confirms whether your email arrives in the inbox, not spam, and verifies SPF, DKIM, and DMARC alignment in real environments.
Review results and update your record if needed. If you see a "failed SPF" result during verification, the issue may lie in a misconfigured include, a third-party provider’s SPF record, or an overly complex setup. Re-evaluate include chains and consider consolidating providers where possible.

Pro tip: avoid over-reliance on static tools

Many online SPF checkers only validate syntax at the DNS level. But they don’t simulate full evaluation. A record that passes a basic check may still fail during actual delivery because of include expansion. That’s why real-world testing matters.

According to RFC 7208, SPF evaluation must stop after 10 DNS lookups. Violating this rule often results in temporary failures (soft bounces) or outright rejection. Tools that simulate this behavior are rare, but essential for high-volume senders.

For developers, the SPF specification (RFC 7208) is the definitive reference. For senders, pairing it with real validation via MailTester's inbox placement tests ensures your message reaches its destination.

Use MailTester's real-time API to verify individual addresses during onboarding or send flows. For bulk lists, bulk verification identifies invalid, risky, or catch-all addresses before sending.

You can catch SPF-related delivery issues early by verifying email addresses before sending. MailTester identifies domains with misconfigured SPF or DMARC policies during real-time checks, and flagging high-risk addresses in bulk lists. This reduces the chance of your messages being rejected or marked as spam due to policy conflicts, especially when senders rely on include mechanisms that expand improperly.

How MailTester’s real-time API detects SPF and DMARC risks

When you use MailTester’s real-time API, it doesn’t just check if an address exists—it observes how the domain responds to verification attempts. If a domain has a broken SPF record or a conflicting DMARC policy, this often shows up as a delayed response, inconsistent verification behavior, or a catch-all detection. These patterns correlate with known issues like include mechanism expansion failures, where nested DNS lookups fail silently, breaking the sender policy.

While SPF itself doesn’t dictate deliverability on its own, a misconfigured policy can trigger rejection by receiving servers. The system treats this as a red flag. You’re not just filtering invalid addresses—you’re filtering domains where sender policy problems may affect your reputation.

Bulk verification uncovers risky domains in your list

Large email lists often include addresses from domains with outdated or malformed SPF records. These domains may appear valid but deliver unpredictably—sometimes bouncing, sometimes being tagged as spam, sometimes not being delivered at all. MailTester’s bulk verification process identifies such lists by measuring high rates of catch-all or invalid addresses, a sign of poor infrastructure or lax policy enforcement.

For example, domains using include:_spf.google.com without proper alignment to their sending IPs can cause validation failures if the include is not properly authorized. When MailTester detects frequent warnings or indeterminate responses from such domains, it flags them as risky. Our 98.9% accuracy helps you remove these addresses before they harm your sender reputation or trigger filters.

By catching these issues early, you avoid the cost of failed deliveries. You can learn more about how our API works here, and see how our bulk verification tool helps clean large datasets: email-list-verify. The goal is simple: send only to domains that have a working, well-configured sending environment.

What’s the best practice for maintaining SPF records as your send stack evolves?

SPF record complexity grows quickly when you include multiple services, especially through the include mechanism. Each include adds a DNS lookup, and records exceeding 10 lookups fail validation entirely.

Keep it simple: limit includes to a single trusted sender or a tightly controlled set of providers. Prefer centralized platforms like SendGrid or Mailchimp that deliver a single, low-lookup SPF record instead of requiring multiple inclusions.

Regular audits after adding new email services are essential. A single unmonitored include can expand your record beyond the limit and break all outbound email. Use tools that validate both structure and lookup count.

Sources

52.1% of the world's top 1.8 million domains (937,931 domains) now publish a valid DMARC record, up from 29.1% in 2023. — EasyDMARC 2026 DMARC Adoption & Enforcement Report (2026)
Google reported 265 billion fewer unauthenticated messages sent to Gmail users in 2024 — a 65% reduction — after its bulk-sender rules took effect, with 500,000+ top domains publishing DMARC records in response. — Google (via MailOver bulk-sender requirements guide) (2024)

Keep reading

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Frequently asked questions

What is the maximum number of DNS lookups SPF allows?

SPF allows a maximum of 10 DNS lookups per record check. Exceeding this limit causes a permanent failure, known as permerror.

Can I use multiple include mechanisms in one SPF record?

Yes, but each include triggers a DNS lookup. Too many can exceed the 10-lookup limit, causing authentication failure.

Does using a redirect instead of include help avoid expansion issues?

No — 'redirect' still triggers DNS lookups from the target domain. It doesn’t reduce the count, just redirects the evaluation path.

How do I fix an SPF permerror when sending emails?

Reduce the number of 'include' directives. Consolidate providers or use a single email service with a low-lookup SPF record.

Can I use SPF with DMARC for better deliverability?

Yes — aligning SPF and DMARC improves inbox placement and reduces reliance on complex SPF chains.

What happens if SPF fails due to include expansion?

The receiving server returns a 'permerror'. Messages are rejected, reducing deliverability and harming sender reputation.

How often should I audit my SPF record?

After adding a new email service or after noticing deliverability drops. Quarterly audits are recommended.

Does MailTester check SPF or DMARC configuration?

MailTester does not directly query SPF or DMARC records. It assesses email address validity and inbox placement risk through real-world delivery tests.

How does email verification help with SPF issues?

By removing domains with high rates of catch-all or invalid addresses, which are often linked to misconfigured SPF policies.

Why should I avoid using multiple third-party email providers without consolidation?

Each provider may require its own 'include' directive, quickly increasing DNS lookup count and risking SPF expansion.

Is there a way to test if my SPF record will cause delivery issues?

Yes — use real-time verification tools like MailTester or test with a tool that simulates the full SPF evaluation process.

What should I do if my email provider uses a high-lookup SPF record?

Use their recommended configuration and avoid adding additional includes. If needed, consolidate services under one provider.