Why Does SPF Pass but the Email Still Fail Verification?

You sent an email. The SPF record passed DNS validation. The tools said it was clean. Yet the message bounced. Or worse—landed in spam. Why?

Because SPF isn’t just about syntax. It’s about policy scope. A record may pass DNS checks, but still fail during actual delivery due to how the include: mechanism expands the sender’s allowed IP list.

Think of SPF as a guest list. The front door checks your ID (DNS syntax). But if you’re on a list that includes a third-party’s entry system—and that system is broken, incomplete, or outdated—the whole list fails at the gate, even if your ID is valid.

Key takeaways

  • SPF can pass DNS validation while still causing delivery failure due to policy expansion via include: mechanisms.
  • Misconfigured or incomplete include: directives expand the policy scope in ways that may reject valid IPs, even if the record is syntactically correct.
  • Failure occurs during message validation, not DNS lookup—meaning SPF records can appear valid but still block delivery.

How Does the include: Mechanism Work in SPF Records?

The include: mechanism in SPF records lets your domain borrow the email-sending authorization policy from another domain by referencing it directly. When a receiving server checks your SPF record, it doesn't just evaluate your own rules — it follows every include: entry, retrieves the referenced domain’s policy, and merges it into a single, expanded SPF policy for validation. This lets you extend trusted sending sources across domains without duplicating rules.

Why Use include: in SPF Records?

Let’s say you run marketing campaigns through a third-party provider like Mailchimp. Their SPF record already specifies which servers are allowed to send on their behalf. You can use include:mailchimp.com in your own SPF record to grant those same servers permission to send on your domain’s behalf. This avoids having to manually list every IP address and keeps your policy more maintainable.

But here's where things go wrong. If you use include: but the referenced domain’s SPF record fails validation — or if it includes a domain that itself contains an invalid or missing include: — the entire SPF evaluation can fail, even if your own domain’s setup is correct. That’s why a simple SPF pass in your own record doesn’t guarantee deliverability: the chain of references must all be valid.

Each include: directive is evaluated recursively. Receiving servers will pull the referenced SPF record, resolve any nested includes, and build a comprehensive policy. If any part of that chain exceeds the SPF limit of 10 DNS lookups (a common threshold), the server may treat the record as invalid, leading to a soft fail or fail, even if the final result seems correct.

The include: mechanism is standard and documented in RFC 7208, the authoritative specification for SPF. It’s widely used, but also a common source of configuration errors — especially in complex setups involving multiple vendors or subdomains.

If you're managing multiple sending sources or using third-party services, testing your SPF chain is critical. A single broken include can cause your legitimate emails to be marked as spam. Use tools that check the full chain of SPF policies, not just the surface record.

Want to validate your SPF setup and find invalid includes before sending? You can test your entire sender policy — including chain dependencies — with our email checker or verify your list at scale with our bulk verification tool.

When Does include: Cause SPF to Fail Despite Passing DNS Check?

Even if your SPF record passes DNS validation, an include: mechanism can still cause a fail if the referenced domain’s SPF policy is invalid, incomplete, or malformed. This happens because SPF evaluates the full expanded policy—not just the direct record. If the included domain lacks proper mechanisms like ip4 or mx, or has a syntax error, the policy becomes non-compliant, leading to a hard fail upon evaluation—even if the include: directive itself looks correct in DNS.

Invalid or incomplete policies in included domains break SPF

Let’s say your SPF record says include:spf.example.com, but spf.example.com has a record like v=spf1 -all or only include:another-domain.com with no actual IP or MX definitions. When the receiver resolves the full policy, it finds no valid mechanisms to authorize your sending IP. Even a single missing or improperly formatted mechanism can cause a strict SPF check to reject the email.

Some receivers, particularly those using modern spam filtering systems, do not just check syntax—they perform full policy evaluation. This means they expand the entire SPF chain and verify each mechanism independently. If any part of the chain fails, the whole check fails. This behavior is in line with RFC 7208’s requirement that SPF policies must be complete and unambiguous to be enforceable.

Why SPF can fail even with a syntactically valid include:

It’s not enough for an include: directive to resolve correctly in DNS. The receiving server evaluates the complete policy chain. If the included domain’s record is malformed—like having multiple v=spf1 tags, or a misconfigured all mechanism—the result is a non-compliant policy, and the message gets rejected.

Even if your own SPF record is clean and passes DNS checks, relying on third-party domains for SPF authorization adds risk. You’re depending on their compliance, and any misconfiguration there can silently sabotage your delivery. This is why thorough SPF testing—beyond just DNS lookup—is essential. It’s not just about syntax; it’s about behavior in actual mail server evaluation.

Using tools that test SPF policies across real-world receivers, like MailTester’s inbox placement tester, helps uncover issues that DNS lookups alone can’t reveal. These real-time checks simulate how mail servers evaluate your full policy, including include: chains.

It’s not uncommon for a domain’s SPF record to pass basic DNS validation while still failing delivery due to expanded policy flaws. To avoid that, ensure all included domains have complete, valid policies. Use tools that enforce full policy evaluation—not just DNS lookup—to catch these hidden failures early.

Common SPF Failures Caused by Misused include: Directives

If your email fails SPF despite having an SPF "pass" due to an include: directive, it’s likely because the included domain either has no SPF record at all, uses a blocking policy, or creates a circular reference. These issues aren’t caught by simple SPF validators — they break evaluation during DNS lookup, leading to soft bounces or rejection with no clear message. Let’s break down exactly how this happens.

Missing or Null SPF in Included Domains

  • You’re using include:trusted-partner.com, but trusted-partner.com has no SPF record — that results in a null policy, which causes SPF evaluation to fail.
  • SPF evaluation treats any domain with no SPF record as “null,” invalidating the entire policy chain. This is standard behavior per RFC 7208.
  • Check the full chain using tools like MxToolbox to trace where an empty policy appears in the chain of includes.

Conflicting or Overly Restrictive Policies

  • Using include: to reference a domain with a policy like ~all (soft fail) or -all (hard fail) can override your own valid policy, causing rejection if both policies aren’t aligned.
  • For example, if your base domain uses include:mailer.example and mailer.example has ~all, the combined policy may appear as soft-fail — acceptable in some implementations, but blocked by aggressive mailers.
  • Always verify the full DNS policy at each included domain’s record, especially if it’s managed by a third party.

Circular Includes and Infinite Loops

  • If Domain A includes Domain B, and Domain B includes Domain A, SPF evaluation hits an infinite loop — but SPF limits the number of include lookups to 10. After that, it stops and results in a permanent failure.
  • SPF processing enforces a recursion limit to prevent denial-of-service scenarios. Circular includes bypass this and cause hard failures even if the syntax is otherwise valid.
  • Use tools such as RFC 7208 (the SPF specification) to validate chains and detect circular references early.

These issues are why real-time SPF validation — not just syntax check — is essential. Tools like MailTester’s verification API can detect these hidden failures before you send, saving you from deliverability black holes.

Properly Testing SPF Policies with Real Email Delivery

If your SPF record passes DNS validation but emails still fail delivery, it’s likely due to a flawed include: mechanism that expands to an invalid policy. SPF evaluation is not just about DNS syntax — it’s about how receiving servers actually evaluate the full policy during delivery. Use tools that test with real IPs and simulate actual SMTP sessions, not just parse records. You need to see if the final policy is valid, complete, and doesn’t trigger a hard fail.

Simulate Real Delivery Conditions

  • Don't rely on DNS-only SPF checkers — they miss how actual mail servers handle policy evaluation during SMTP handshake.
  • Use tools that perform real email delivery tests from verified IPs to see how SPF is enforced in practice.
  • MailTester’s inbox placement tester simulates real delivery paths and returns accurate SPF, DKIM, and DMARC results as seen by inbox providers.
  • Check for common issues like missing include: mechanisms that expand to invalid domains, or overly complex policies that exceed the 10 mechanism limit.

Check the Final Expanded Policy

  • Always inspect the final expanded SPF policy after all include: and redirect: mechanisms are resolved.
  • A single invalid mechanism (like include:invalid.example.com) can cause the entire policy to fail, even if the DNS record itself is parseable.
  • Tools that only validate the original record miss these chain failures. You need a solution that resolves and evaluates the full policy.
  • Use MailTester’s email checker to test individual addresses with real-world SPF behavior, not just syntax.
  • Per RFC 7208 Section 6.2, receiving servers must evaluate the full policy — not just the original record — so validation must reflect this.
SPF is not a static DNS record check. It’s a dynamic evaluation that happens during SMTP. If you only validate syntax, you’re blind to delivery failure causes.

How MailTester Handles SPF Failures Caused by include:

SPF pass but email fails? That’s often because of a broken include: mechanism in your SPF record. MailTester detects these issues by analyzing the full expanded policy—checking every domain referenced in include:—not just the syntax. If a referenced domain has no valid SPF record or returns a temporary DNS error, the entire policy fails during real email delivery. Basic DNS tools miss this because they only validate the record’s structure, not its actual behavior under real-world sending conditions.

Why Simple SPF Checks Fall Short

Many tools just scan for syntax errors or validate your SPF record in isolation. But SPF doesn’t work in a vacuum. Each include: directive pulls in another domain’s policy. If that domain’s SPF record is missing, malformed, or returns a DNS timeout (like TempError), the validation fails—even if your own record looks correct. The RFC 7208 specification makes this explicit: the evaluation must account for all included policies during actual delivery attempts.

MailTester simulates real delivery by expanding the full policy, including every include: target, and then testing the result against sending IPs. This catches the kind of failure that only appears when an email client actually tries to send, not when a static DNS lookup runs.

How We Catch Hidden SPF Failures

Let’s say your SPF record includes include:_spf.google.com. A basic checker sees that and says “valid.” But if Google’s SPF record is outdated, missing, or misconfigured, the inclusion causes failure at delivery time. MailTester checks that target during validation. If it fails a DNS lookup or returns a permanent error, that’s flagged as a critical SPF failure—even if the base record passes.

This is why sending to an address with a valid SPF record can still get blocked. The problem isn’t with the recipient’s address—it’s the invisible dependencies in your SPF chain. With MailTester, you’re not just checking syntax; you’re validating what actually happens when your email leaves your server. We use the same real-time verification stack used by top senders to test inbox placement and sender reputation.

Want to validate a list before sending? Use our bulk email verification to catch SPF issues across thousands of addresses. Or test individual addresses with our email checker to detect issues early. You get an honest verdict: valid, invalid, catch-all, or risky—with clear reasoning.

Step-by-step: Fixing SPF Failures from include: Mechanisms

If your SPF record passes validation but emails still fail SPF checks, the issue likely lies in an include: mechanism referencing a domain with a broken, conflicting, or missing SPF record. You must validate the full policy, verify each included domain’s SPF record, and replace broken references with explicit, working entries. Only then can you ensure your sending domain passes authentication.

Use a real SPF validator to expand the full policy

  1. Retrieve your full SPF policy using a tool like MXToolbox or MailTester’s SPF validation API. These tools expand include: directives to show the complete policy, revealing hidden issues.
  2. Examine each included domain listed in include: mechanisms. For example, if your record includes include:spf.example.com, check that domain’s SPF record directly — not just the parent record.
  3. Confirm all included domains have valid, properly formatted SPF records. A single domain without an SPF record, or one with a malformed policy (like too many mechanisms or no allow), can cause failure even if the parent record passes.
  4. Look for conflicts such as multiple all mechanisms, missing allow (a common mistake), or records exceeding the 10 mechanism limit. These break SPF evaluation.
  5. Replace problematic include: entries with explicit ip4: or ip6: entries if you control the IP addresses. If not, remove the include: if the domain isn’t essential to your sending setup.
  6. Test the new policy using a delivery simulator that checks real sending IPs and real-time DNS lookup. Tools like MailTester’s inbox placement test simulate inbound delivery from major providers, catching failures that validators miss.

Verify consistency across the chain

SPF is evaluated recursively. If one included domain fails validation due to a missing include:, an incorrect all mechanism, or a record longer than 255 characters, the entire policy fails — regardless of the parent record’s validity. Always test in context.

According to RFC 7208, a receiving mail server applies SPF rules in sequence. If any include: results in a failure, the entire policy fails. This is why chain validation matters. No tool can predict every edge case — but you can catch the most common failures by validating each hop.

Pro tip: Use MailTester’s in-app AI assistant to review SPF records and flag common issues like include: loops or missing allow. It won’t fix your record, but it will point you toward the right changes.

The Real-World Impact of Faulty include: Mechanisms on Deliverability

Even if your SPF record passes basic syntax checks, a flawed include: directive can still block your emails from reaching inboxes—especially with Gmail and Microsoft’s receivers, which enforce full, real-world validation. A single misconfigured included domain can cause outright rejection or quarantine, even if your own record is technically correct. This is why SPF isn't just about syntax; it's about chain integrity.

Why "Valid" SPF Can Still Fail in Practice

SPF validation isn't a simple pass/fail on your domain’s record. Major providers like Gmail and Outlook perform deep evaluation: they resolve every include: and redirect: mechanism, checking each linked domain's SPF policy in real time. If any included domain has a malformed or invalid record, the entire chain fails, and the message is treated as untrusted.

Let’s say you use include:_spf.google.com but it resolves to a defunct or misconfigured domain. Even if your record is valid on paper, receivers won’t look past it. The result? Bounces, soft fails, or messages landing in spam. This isn’t theory—RFC 7208 (the updated SPF standard) explicitly outlines this recursive evaluation process.

How Faulty Includes Break Delivers, Not Just Checks

Many senders assume “SPF pass” means safe delivery. But the reality is more nuanced. You can pass DNS-level validation yet still fail in production because an included domain’s record is missing, contradictory, or too complex. Microsoft’s spam filtering systems, for example, use this as a red flag for suspicious sender behavior.

Even if your domain has a valid SPF record, a single broken include:—like one pointing to a legacy service or a defunct partner—can trigger rejection. This is especially common in email ecosystems where third-party platforms (like CRMs or marketing tools) are baked into SPF policies without oversight.

That’s where proactive verification helps. Before sending at scale, test the full SPF chain. Use an advanced tool to validate not just your record, but every include: domain’s response. You can audit your list of included domains and catch problems before they impact your sender reputation.

MailTester’s bulk email verification includes SPF and DNS health checks across your list, flagging domains with broken or invalid SPF chains—including faulty include: directives—so you can clean your list before sending.

What SPF, DKIM, and DMARC Really Do for Deliverability

SPF, DKIM, and DMARC are the backbone of modern email authentication. SPF checks if the sending IP is authorized by the domain’s policy. DKIM confirms the email body and headers weren’t altered in transit. DMARC combines both results, enforces policies like quarantine or rejection, and ensures alignment between the sender’s domain and the authenticated identity. If any one of them fails — even if SPF passes — deliverability can drop significantly. It’s not enough to pass SPF alone when a domain has include: mechanisms or complex setups.

Why SPF Pass Doesn’t Guarantee Delivery

SPF doesn’t just check the IP address; it evaluates the full chain of sender policies, especially when include: mechanisms are used. If a domain references another domain (like include:spf.example.com), the entire policy chain must resolve correctly. A misconfigured include or an outdated policy can result in SPF pass locally but fail in real-world validation by receiving mail servers.

Let’s say you use SendGrid and have an SPF record like spf1 include:sendgrid.net -all. That’s valid in theory. But if SendGrid’s public policy has changed and your record hasn’t been updated, or if a third-party service you’ve included in the chain is no longer trusted, your email may still be rejected. This is why having SPF pass in a test tool doesn’t mean it will always pass in production.

SPF checks are based on the IP address of the sending server at the time of delivery. But if the sending infrastructure uses shared or dynamic IPs, or relays through multiple intermediaries, SPF can fail even if the policy appears correct. This is especially common with cloud-based senders, resellers, or legacy systems that don’t properly set up authentication chains.

How DKIM and DMARC Prevent Misuse and Improve Trust

DKIM prevents message tampering. It adds a cryptographic signature to the email headers and body. When the receiving server checks it, it verifies both the integrity of the message and that it was signed by a domain with the correct private key.

DMARC ties SPF and DKIM together. It defines what to do when either fails. For example, a DMARC policy of rua=mailto:[email protected] and p=reject means emails failing either authentication check will be rejected. This protects against spoofing and forces senders to fix broken setups.

Even if SPF passes, DKIM is independent. A message can pass SPF (IP authorized) but fail DKIM (signature invalid or altered) — and that’s enough to trigger rejection or junk filtering. Alignments in both SPF and DKIM must match the domain in the “From” field. Mismatched headers, forwarded emails, or mailing list relays often break this alignment.

Real-world deliverability depends on all three aligning. According to the Authentication, Visibility, and Accountability (AVA) report by the Messaging, Malware, and Mobile Anti-Abuse Working Group (M3AAWG), emails that fail any one of SPF, DKIM, or DMARC are significantly more likely to end up in spam folders. You can test your sender configuration with MailTester’s inbox placement tester to simulate real inbox delivery and catch hidden issues before sending at scale.

Use MailTester to Catch SPF Failures Before They Hurt Your Inbox Placement

Emails that pass SPF in theory may still fail in practice due to misconfigured include: mechanisms, especially when combined with relaxed policies or improper DNS delegation. These issues often go undetected until they impact deliverability.

How MailTester Prevents These Issues

Unlike basic checks, MailTester evaluates SPF policies in real-world context — including all included domains, expanded rules, and actual IP alignment across major mail providers.

Its 98.9% accuracy is achieved by simulating actual delivery conditions, catching failures before they harm sender reputation or reduce inbox placement.

Automated Verification at Scale

With real-time API and bulk list verification, MailTester identifies problem addresses — including those failing SPF due to include: mechanisms — before they’re sent.

Whether you're syncing with Mailchimp, HubSpot, Klaviyo, or SendGrid, MailTester ensures only validated, deliverable emails reach your audience.

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Frequently asked questions

Why does my SPF pass DNS check but still fail email validation?

SPF DNS checks only validate syntax. Failures often come from the include: mechanism referencing a domain with an invalid or missing SPF policy. MailTester checks the full policy evaluation.

Can include: cause SPF to fail even if the record is correct?

Yes. If an included domain has no valid SPF record, the expanded policy becomes invalid. Even syntax-valid records can fail during real-world evaluation.

How do I know if my include: directive is broken?

Test the full expanded SPF policy using a tool like MailTester or MXToolbox. Ensure all included domains have valid, properly configured SPF records.

Is using include: risky for SPF policy?

Yes — if any included domain has an invalid or missing SPF record, the entire policy can fail. Always validate all referenced domains in your SPF chain.

Does MailTester detect include: mechanism issues?

Yes. MailTester evaluates the complete expanded SPF policy, including all referenced domains, and flags issues caused by include: mechanisms.

Can SPF fail even with DMARC in place?

Yes. DMARC relies on SPF and DKIM. If SPF fails due to an include: issue, DMARC will also fail, even if the DMARC record is valid.

How does MailTester help with deliverability testing?

It simulates inbox placement by testing actual sending IPs, SPF policies, and delivery across major email providers — not just DNS checks.

Do SPF failures due to include: affect sender reputation?

Yes. Consistent SPF failures lead to lower reputation, increased bounce rates, and higher risk of being flagged as spam.

Should I avoid using include: in SPF records?

Not necessarily, but only if all referenced domains have valid, secure SPF policies. Prefer explicit mechanisms when possible to reduce risk.

How can I test SPF policy expansion safely?

Use tools like MailTester or MxToolbox to expand and validate the full policy. Never test in production without simulation.

What happens if I have a circular include: in my SPF?

It causes policy evaluation failure. Most mail servers reject messages with circular references, even if syntax is valid.

Can a catch-all email address pass SPF but still fail delivery?

Yes. A catch-all may pass SPF but fail due to content, reputation, or message content filters. MailTester flags such addresses as 'risky'.