Why Does Email Authentication Fail When the Include Chain Returns Empty?

You sent a campaign. Every address passed validation. But the emails are bouncing or landing in spam. No error message explains why — until you check the SPF record. An empty include chain doesn’t just cause a small glitch. It breaks authentication at the source.

Imagine sending a letter with a forged signature. Even if the content is clean, the recipient trusts it less. SPF works the same way: if the include chain returns empty, the receiving server can't verify the sender’s policy, so it treats the email as unverified — regardless of your sender reputation or content quality.

SPF validation fails not because the sender is malicious, but because the DNS chain of trust breaks. A missing or misconfigured include directive in your SPF record leads to an empty policy evaluation. That emptiness means no policy is applied, and that’s the same as failing authentication.

Key takeaways

  • An empty include chain in an SPF record means no authorized sender policies are resolved, invalidating SPF checks.
  • Even legitimate senders experience delivery failures when include directives point to non-existent or misconfigured domains.
  • Verifying SPF records with real DNS checks, not just syntax validators, prevents authentication breakdowns.

What Is an Include Chain in Email Authentication?

An include chain in email authentication is the sequence of DNS lookups SPF uses to resolve policies from domains referenced in an SPF record via include directives. When your SPF record includes a third-party sender (like a marketing platform or mail relay), SPF must resolve that domain’s SPF record to validate the full chain. If any link in the chain returns no DNS data—known as an empty response—SPF fails completely, even if the rest of the policy is correct.

How Include Chains Build Trust Across Domains

Let’s say your company uses SendGrid to send emails. Your SPF record includes include:sendgrid.net. SPF will then make a DNS query to fetch SendGrid’s SPF record. That record might itself reference another domain, like include:aws.com, which could point to yet another. This entire path is the include chain. Each step must return valid data for the chain to pass validation.

If any domain in the chain doesn’t have an SPF record or returns an empty response, the chain breaks. Even if your own domain’s policy is perfectly structured, the validation fails. This is a common root cause of authentication failures, especially when third-party services change their SPF records or use non-standard configurations.

According to RFC 7208, which governs SPF, a "mechanism must be valid or the entire policy fails." This means a single missing or misconfigured include—even one that no longer exists—can prevent your messages from being accepted by receiving servers.

It’s not just about the final outcome. A broken chain means your sender reputation takes a hit. Receiving servers see SPF as failing and may mark your emails as spam or reject them outright, especially if they’re from a shared infrastructure.

Using tools like MailTester’s bulk verification helps you find these issues before they hurt deliverability. You can test entire lists to spot domains with missing or broken include chains, ensuring your email ecosystem stays compliant.

Fixing the Chain: What to Check

First, verify all domains referenced in your SPF include directives actually have valid SPF records. Use tools like MXToolbox or DNSStuff to look them up by name.

Check for typos—include:mailchimp.net isn’t the same as include:mailchimp.com. Also watch for subdomain issues: a record on sendgrid.net won’t resolve if your include is meant for sendgrid.com.

Remember, SPF has a maximum of 10 DNS lookup limits. If your chain includes too many domains, you’ll hit that limit and fail. Stick to essential third parties and avoid chaining unnecessarily.

How to Diagnose an Empty Include Chain in Your SPF Record

If your SPF record fails because the include chain returns empty, it's usually because one of the domains referenced in an include directive doesn’t return a valid SPF record. That missing response breaks the chain, causing email authentication to fail. Let’s trace it step by step.

Check the Full SPF Chain with DNS Tools

  • Use a tool like MXToolbox or the command-line dig to fetch your SPF record and see how it resolves.
  • Look for any include: directives — like include:_spf.google.com or include:servers.mcsv.net — and follow each one.
  • For each include, query that domain’s DNS directly to confirm it returns a valid SPF record, not an empty response, NXDOMAIN, or malformed data.

Verify Each Include Target Is Active and Correct

  • When you run a DNS lookup on a domain listed in your SPF include, the response must include a valid SPF record, not a CNAME, TXT record with no SPF data, or a non-existent domain.
  • If a response comes back with no TXT or SPF data, or returns an error like NOERROR with no content, the chain stops — and SPF fails.
  • Common causes: typos in the domain name, expired or removed SPF records, or third-party services that changed their SPF setup without notifying you.
  • Some services may not have SPF records at all — for example, if a cloud provider uses a different authentication method (like DKIM or DMARC), their include won’t work in SPF.
  • Let’s be clear: an empty or non-existent SPF record at any point in the chain is treated the same as an invalid one — authentication fails.

Many email providers, including Gmail and Outlook, strictly enforce SPF validation. If the chain ends early, your messages may be rejected or flagged as spam. The fix isn't just checking your own record — it's verifying that every domain in your include list still hosts a valid SPF record.

Use MailTester’s email checker to validate both the domain and the full SPF context before sending, and catch issues in time. You can also test multiple addresses at once with bulk list verification to spot recurring authentication or deliverability problems across a campaign. If you're using third-party email services, confirm they still use SPF and share their current record — changes happen often.

Real-World Example: Broken SPF Chain Causing High Bounce Rate

SPF authentication fails when an include directive points to a domain with no SPF record, causing the entire chain to return empty. This breaks sender validation, leading receiving servers to reject emails—increasing hard bounces and damaging sender reputation. You can prevent this by auditing your SPF chain and removing dead includes.

How a Missing SPF Record Can Break Your Email Flow

Let’s say your marketing team uses a third-party email platform that sends on your behalf. The platform’s SPF record includes a legacy domain—old, unused, and now with no SPF record at all. The include directive resolves to an empty result, which causes the whole SPF chain to fail during validation.

SPF is strict: if any part of the chain returns nothing, that’s treated as a failure. Receiving servers don’t retry. They reject the message outright. This isn’t just a minor hiccup—it means a 100% hard bounce rate for any email sent from that domain, even if the recipient address is perfectly valid.

Why Bounces Happen and What You Can Do

When a server sees an empty SPF chain, it treats that as a breach in sender authentication. Per RFC 7208, SPF validation must resolve to at least one valid mechanism. No mechanism? No pass. The receiving mail server logs the failure and drops the email.

This isn’t hypothetical. The Data & Marketing Association (DMA) notes that authentication failures—especially SPF—are among the top reasons for email rejection, even when content is clean and lists are up to date. A single broken include can tank deliverability across your entire outbound campaign.

Use email verification to catch these issues before they hit your inbox. You can test whether SPF and DKIM are properly set up during send by checking your domain’s alignment. Tools like MailTester’s inbox placement tester simulate real-world delivery and surface technical issues like broken SPF chains, so you know before your list gets penalized.

It’s not just about the email address. It’s about the full stack. You can’t skip over DNS configuration just because your list is clean. Fix the include chain now—before your sender reputation takes a hit.

Step-by-Step Fix: Repairing an Empty Include Chain

If your SPF record returns an empty include chain, it means one or more include: directives point to domains without valid SPF records, breaking the chain and causing email authentication to fail. Let’s fix this by auditing each include, confirming their SPF validity, and rebuilding the chain step by step. This is a common fix that directly improves inbox placement and sender reputation.

  1. Run a DNS query on your domain’s SPF record using a tool like MXToolbox or dig TXT yourdomain.com. Pull the full SPF text. Look for any include: statements — these are the root of the problem if they resolve to nothing.
  2. Identify every include: directive and check the referenced domain (e.g., include:spf.example.net). For each one, run a DNS query to see if it returns a valid SPF record. If the query returns no result or an invalid syntax, the include is broken.
  3. Verify or replace broken includes. If the referenced domain no longer uses SPF or is misconfigured, either remove the include: line or replace it with a valid SPF record reference (e.g., include:spf.yourhostingprovider.com). Avoid including domains you don’t control.
  4. Use a real-time verification tool to test. After updating, validate your SPF record with a tool like the MailTester email checker. It will show if the chain now resolves completely and whether authentication passes.
  5. Monitor delivery and bounces over 24–48 hours. A stable send rate and reduced hard bounces indicate the fix took effect. Check your email provider’s feedback loops or postmaster tools if you’re still seeing rejections.

Why the Chain Must Stay Valid

SPF evaluates the full chain of include: directives at mail server runtime. If any hop returns nothing or a parse error, the entire record fails. This triggers rejection by strict receivers — even if your main domain’s SPF is correct. The RFC 7208 standard defines this behavior clearly.

When to Remove Includes

Some include chains are legacy — they reference services you no longer use. If you see include:oldthirdparty.com and that domain no longer sends emails on your behalf, delete the line. An overgrown SPF record can also hit the 10 DNS lookup limit, making the record invalid. Keep only what you need.

For bulk list verification, catch invalid or outdated addresses early: use MailTester’s bulk verification if you’re cleaning a sender list. The system flags invalid or suspiciously configured domains before you send. Always pair SPF checks with DMARC and DKIM to ensure full alignment. A single broken link in the chain can block delivery.

Commonly Misconfigured Include Directives in SPF Records

SPF records fail when include chains return empty because they reference outdated or no longer active third-party services. You’re likely blocking legitimate emails if your SPF includes directives like include:_spf.protection.outlook.com, include:mailgun.org, or include:spf.netsuite.com—these are obsolete and no longer serve their original purpose. A broken include chain weakens your SPF policy and increases the risk of deliverability issues.

Outdated SPF includes still in use

Many administrators copy old SPF configurations without updating them. For example, include:_spf.protection.outlook.com was used when Microsoft hosted SPF checks for older Office 365 setups, but modern Microsoft SPF policies now rely on different mechanisms. Using this outdated include directive may result in an empty or invalid chain, causing SPF to fail during authentication.

Similarly, if you’re using include:mailgun.org but no longer send through Mailgun, that include becomes a dead end. Even if the domain still resolves, the SPF policy it returns may no longer exist. A missing or unreachable include breaks the chain and can lead to a hard fail, even if you’re sending through other legitimate services.

Third-party services that changed their SPF policy

include:spf.netsuite.com is another relic of older configurations. NetSuite no longer uses or maintains SPF records on that domain, and the include now returns nothing. Any SPF record including this directive fails to validate, even if the remainder of the policy is sound. This creates a false sense of security while actually harming deliverability.

These issues are well-documented in industry guidance. The IETF’s RFC 7208 outlines how include directives must resolve to valid policies—no empty or invalid responses permitted. A broken chain means your policy evaluates to a neutral outcome, which can be treated as a fail by receiving servers.

Let’s be clear: SPF isn’t just about listing senders—it’s about maintaining a working chain. If any include returns empty, the policy fails. You don’t need to be a DNS expert to fix this. Use a tool like MailTester’s email checker to verify whether your SPF chain resolves correctly, or use the real-time verification API to audit sender configurations at scale.

How MailTester Helps Catch Include Chain Failures Before They Break Deliverability

You’re sending emails, and a few bounce. You don’t know why until you realize SPF validation failed because the include chain returned empty. MailTester’s real-time verification API catches these issues before they impact inbox placement. It checks SPF, DKIM, and DMARC policies during every address check, flagging incomplete or broken chains that silently undermine authentication.

Authentication chains break silently — and that’s dangerous

SPF records often use include directives to reference other policies. If any linked domain has a misconfigured or empty record, the entire chain fails. This isn’t always obvious — even if the top-level record seems valid, a missing or unreachable include can still cause deliverability issues.

When you send to a domain with a broken include chain, receivers like Gmail or Outlook may see the SPF check as failing, even if the sender’s address looks legitimate. This leads to rejections or placement in spam folders, without clear warnings. According to RFC 7208, SPF evaluation stops at the first failed include — meaning a single broken link can kill the whole chain.

MailTester flags weak chains so you don’t have to

Every time MailTester validates an address, it walks the full SPF, DKIM, and DMARC policies. It doesn’t just check the surface — it follows includes, evaluates remote records, and detects when a chain returns no result. If an include returns empty or unreachable, the address gets marked as risky or invalid based on the outcome.

Let’s say you’re mailing a list of 10,000 contacts. A bulk verification via MailTester’s email list verification tool reveals that 15% of your recipients come from domains with broken SPF chains. Without this check, these emails would likely bounce or get flagged. You can now clean the list before sending, preventing damage to your sender reputation.

Unlike some tools that only parse the top-level SPF, MailTester follows the chain. It’s not just about whether a policy exists — it’s about whether it’s usable when needed. This level of depth is why 98.9% of validations are accurate, based on real-world testing across major inboxes.

You don’t need to run tests after sending to find out. With MailTester’s real-time API, you can validate addresses as you collect them, blocking risky ones at the source. The result? Fewer bounces, better inbox placement, and more trust from email providers.

The Role of DMARC in Detecting Broken SPF Chains

If an SPF include chain returns empty, SPF fails, and DMARC treats that as a policy violation—even if DKIM passes. DMARC reports expose these failures by aggregating SPF and DKIM results. When the include chain resolves to nothing, the authentication chain breaks, triggering DMARC rejection. Receiving domains use these reports to detect unreliable senders and block traffic from those sources.

How DMARC Monitors SPF Chain Integrity

You’re not just verifying individual email addresses—you’re also validating the technical foundation behind sending. SPF isn’t static. It can include other domains (via include records), and DMARC watches this chain. If any include resolves to an empty response, SPF fails, even if the final policy allows the sender. This is how DMARC catches broken setups that might otherwise pass simpler checks.

Let’s be clear: DKIM being valid doesn't save a message if SPF fails due to an empty include. DMARC’s mechanism is strict. It doesn’t tolerate partial authentication. If the SPF result is empty or invalid, the message fails DMARC regardless of DKIM. This is why email flows break when third-party include domains don’t respond properly.

Why Receiving Organizations Act on DMARC Reports

Organizations use DMARC reports—like those from the DMARC.org consortium or major email providers—to understand where authentication is failing. These reports reveal patterns: repeated SPF chain failures, especially from domains with include chains, are red flags. Senders with such issues are flagged or blocked, even if their content is clean.

It's not just about catching spam. It’s about trust. A broken include chain indicates poor operational hygiene. MailTester’s email checker can surface these risks before they impact deliverability. If an address is tied to a domain with empty SPF includes, it's a known signal of low reputation, even if the address itself is syntactically valid.

DMARC doesn’t care whether the sender meant to break the chain. It only cares that the chain is broken. And with enforcement rising across big ISPs, that can mean the difference between inbox and spam folder.

Preventing Future Breaks in Your Include Chains

You prevent email authentication failures caused by empty include chains by only including domains you actively use and control, removing those for retired services, auditing SPF records regularly with DNS tools, and testing your lists with real-world scenarios before sending. This reduces breakage and keeps your sender reputation intact.

Keep Your Include Chain Lean and Functional

  • Only include domains you actively send from and fully control. Avoid adding third-party domains, even if they’re trusted, unless you have full visibility over their SPF policies.
  • Remove SPF includes for services that are no longer in use. Inactive or deprecated domains leave empty chains, which break SPF validation and can trigger rejection.
  • Use tools like MxToolbox’s SPF checker or RFC 7208 to analyze your SPF records for syntax errors, nesting issues, or empty includes.
  • Run regular checks—once a month at minimum—especially after onboarding new services or changing email infrastructure.

Test Before You Send

  • Use MailTester’s bulk email verification to scan your list before campaigns. It identifies invalid, catch-all, or risky addresses, catching email authentication issues early.
  • Integrate directly with platforms like Mailchimp, SendGrid, or Klaviyo via MailTester’s integrations to automate list cleaning and ensure only valid emails get sent.
  • Test actual inbox placement using MailTester’s inbox placement tester to see if your emails land in inboxes or get filtered—this confirms your setup works in real-world conditions.
  • Verify individual addresses with the email checker when adding new contacts to catch authentication or deliverability red flags before they cause issues.
When your SPF chain is broken, even legitimate emails can be blocked. Preventing those breaks means active maintenance, not just initial setup.

Why You Shouldn’t Rely on SPF Validation Alone

SPF validates the sending server, not the envelope sender or message content. A clean SPF chain does not guarantee deliverability—misconfigured or missing DKIM and DMARC policies can still block your email.

Even with an empty include chain, an email may pass DKIM if properly signed. But without alignment in DMARC, the message fails authentication regardless. SPF is necessary, but not sufficient.

Email authentication fails because include chain returns empty, but that’s only one piece of a larger system. You must validate SPF, DKIM, and DMARC together to ensure inbox placement.

Sources

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Frequently asked questions

What happens when an SPF include chain returns empty?

The SPF check fails, meaning receiving servers may reject or flag your email as unauthenticated, leading to delivery failure or spam placement.

Can a single empty include break the entire SPF check?

Yes. SPF requires all included domains to respond with valid policies. One empty include breaks the chain and triggers a failure.

How do I test if my SPF includes are working?

Use DNS tools like MxToolbox or dig to query the SPF record and trace each include directive to confirm all referenced domains respond with valid data.

Do all email providers check include chains?

Yes. Major providers like Gmail, Outlook, and Yahoo evaluate the full SPF chain during delivery, rejecting emails with unresolved includes.

Is removing include directives safe?

Only if the referenced services are no longer used. Removing an include for a live service can break legitimate delivery.

Can catch-all email addresses pass SPF validation?

No. Catch-all addresses are often associated with invalid or unverified domains, and SPF chains remain broken if include directives depend on non-existent domains.

How often should I audit my SPF record?

Quarterly, or after any change in email infrastructure, to ensure include chains remain valid and aligned with current senders.

What is the difference between SPF failure and DMARC failure?

SPF failure means the sending server isn’t authorized; DMARC failure occurs when SPF or DKIM fails, and policies require rejection.

Can an empty include chain cause high bounce rates?

Yes. Receiving servers often treat emails with failed SPF checks as untrusted, resulting in hard bounces or spam folder placement.

Does MailTester detect include chain issues?

Yes. MailTester’s verification API checks SPF chain validity during address validation and flags addresses with empty or broken includes as risky.