SPF 'include' Not Resolving

Why does SPF 'include' fail to resolve during verification with DANE enabled?

You're verifying an email address, and the system says it’s valid—but the SPF 'include' directive fails to resolve during DANE validation. Why? Because DANE checks TLS security, not DNS policy chains.

SPF 'include' relies on external lookups to confirm a domain’s authentication policy. But when DANE is active, the verifier validates TLSA records at the transport layer—without resolving those same external SPF includes. The result? False negative flags for legitimate addresses.

DANE enforces secure transport. SPF enforces sender reputation. They’re not the same layer. When one blocks the other, even valid inclusions fail to resolve.

Key takeaways

DANE validates TLSA records for encrypted transport but does not resolve SPF 'include' mechanisms.
SPF 'include' fails if the target domain has no valid SPF record or is unreachable—regardless of DANE status.
False negatives in email verification often stem from layer mismatches: DANE secures transport, but SPF governs sender policy.

How DANE affects DNS-based email verification workflows

When DANE (DNS-based Authentication of Named Entities) is enabled, TLSA records validate that a certificate binding is correct, which secures the encrypted connection. However, this doesn’t automatically verify SPF policy alignment—tools must still independently check SPF records, as DANE does not replace SPF validation. Skipping SPF lookup after DANE can cause false positives in verification, leading to undetected invalid or risky addresses.

DANE’s role in securing TLS, not email policy

Let’s be clear: DANE validates that a TLS certificate matches its domain via DNS-based TLSA records, as defined in RFC 6698. This is about encryption integrity, not sender authentication. A valid TLSA record means the connection is secure—but it tells you nothing about whether the sending domain is authorized to send email for that address.

Verification engines that assume “secure TLS = valid sender” risk misclassifying spoofed or invalid addresses. For example, a mail server might have a valid TLS certificate but still be unauthorized to send from a given email address. Relying on DANE alone for verification breaks the chain: you’ve secured the channel, but not confirmed the source.

Why SPF must still be resolved—even with DANE

SPF is a separate mechanism that defines which mail servers are authorized to send for a domain. DANE can’t replace it. When a verification process skips SPF record lookup after DANE validation, it fails to detect misconfigured or impersonated sending sources.

Imagine a domain with a valid TLSA record, but its SPF record is empty or misconfigured. Without checking SPF independently, the engine might mark the domain as valid—even if the sending server isn’t authorized. This results in delivery failures, increased bounce rates, or even reputational harm from sending to compromised addresses.

Robust verification tools like MailTester’s bulk verification maintain multiple independent checks: DNS policies (SPF, DKIM, DMARC), mailbox existence, catch-all detection, and transport-layer security—all in parallel. This layered approach prevents single-point failures from tools that prioritize DANE at the expense of policy verification.

Even if you’re using DANE for transport security, never assume it covers sender validation. It doesn’t. You need both.

What happens when SPF 'include' doesn’t resolve during a real-time verification?

When an SPF include directive fails to resolve during verification, the domain’s SPF record is treated as incomplete or broken. This triggers a reliability flag—even if the email address itself is valid—because receiving servers cannot verify sender authorization. Without a working SPF policy, the sender’s domain is treated as untrustworthy, increasing the risk of rejection or spam filtering.

Why SPF is critical in real-time email verification

SPF, or Sender Policy Framework, is a core email authentication method that tells receiving servers which mail servers are authorized to send on behalf of a domain. If the SPF record contains an include directive that points to a domain with malformed DNS, missing records, or a DANE validation failure, the entire policy may fail to resolve. This breaks the chain of trust expected by modern email systems.

For example, if your SPF includes a third-party domain like include:_spf.example.net but that domain has a DANE (DNS-based Authentication of Named Entities) validation that fails due to a mismatched certificate or expired trust chain, the include is effectively ignored. The verification system sees no valid authorization path, even if the email address is perfectly structured.

False positives and their impact on deliverability

Without a working SPF policy, real-time verifiers like MailTester mark the domain as unreliable—even if the individual email address is valid. This leads to false positives: good email addresses are rejected not because they’re wrong, but because their domain’s SPF chain is broken.

According to RFC 7208, SPF record evaluation stops at the first unresolved include. This means a single failure cascades into an entire domain being deemed untrusted. In practice, this can mean legitimate marketing emails, transactional messages, or customer receipts silently failing to reach inboxes.

MailTester detects these failures during real-time verification by attempting to resolve all includes in the SPF record, simulating how major email providers (like Gmail, Outlook, and Yahoo) evaluate sender reputation. You can test this behavior on your own list using our bulk verification tool, which flags domains with broken SPF includes and provides actionable feedback.

How MailTester handles SPF 'include' resolution despite DANE validation

MailTester resolves SPF includes independently of DANE validation by performing real DNS queries for both the main domain and every included domain recursively. It doesn’t rely on DANE’s cryptographic validation to determine SPF policy, because SPF and DANE serve different purposes and operate on different protocols. Even if DANE validation passes, MailTester still checks each 'include' domain’s actual SPF record to catch misconfigurations.

Independent SPF Policy Resolution

Let’s be clear: DANE does not replace SPF. DANE secures DNSSEC validation of TLSA records; SPF is about sender authentication via DNS TXT records. A DANE success doesn’t mean an SPF policy exists. MailTester doesn’t assume this. It queries the full SPF chain.

For each 'include' directive, it makes a real-time DNS lookup. If the included domain has no SPF record, or if the record is malformed, MailTester flags the entire chain as risky—not invalid. This means the address might still deliver, but it’s not reliably authenticated, which affects sender reputation and inbox placement.

Risk Over Block: Accuracy First

Why risky instead of invalid? Because blocking entirely would hurt legitimate senders with incomplete but functional SPF configurations. The goal isn’t to block — it’s to inform. A risky flag means you should review the inclusion chain before sending.

For example, if your list includes a user from a marketing partner whose domain doesn’t publish SPF, that’s not a dead end—it’s a red flag. You can still send, but you’ll carry higher delivery risk. This granularity is why MailTester’s 98.9% accuracy comes from respecting real-world complexity, not over-simplifying it.

As RFC 7208 (the SPF spec) outlines, SPF policies are evaluated based on all included records, not just the primary one. MailTester follows that principle, even when cryptographic validation like DANE passes. This ensures you don’t miss configuration gaps.

Use MailTester’s bulk verification to check entire lists, or test individual addresses with our email checker, which surfaces these SPF issues in real time before you send. The system works whether DANE is enforced or not—because it’s not meant to replace SPF, just to verify it correctly.

Step-by-step: what happens during an SPF verification in MailTester

When you verify an email address, MailTester checks its SPF record in full — not just the top-level domain, but every include directive recursively. It resolves each included domain, validates the SPF policy, and scores the entire chain. If a linked domain fails validation (like a DANE-validated domain that doesn’t support SPF), the whole path is flagged as risky or invalid. This prevents you from assuming an address is safe just because the parent domain passes.

Let’s break down the flow

Parsing the email syntax and domain — MailTester checks that the address is correctly formatted (e.g., [email protected]) and matches standard RFCs. Invalid syntax fails immediately. This step catches typos like user@@example.com or missing domain parts.
Retrieving the SPF DNS record — A DNS query retrieves the SPF TXT record from the domain’s authoritative name server. If no record exists, the result is marked as no policy.
Resolving 'include' directives recursively — For each include: tag in the SPF record (e.g., include:_spf.google.com), MailTester makes a new DNS lookup. This happens for every included domain, no matter how deep the chain.
Validating each included domain's SPF policy — For every resolved domain, MailTester checks whether it has its own SPF record. If the included domain has no valid SPF, or if the record is malformed, the chain is considered risky. This includes cases where DANE validation blocks SPF checks, but the domain is still in the chain — a known issue in some secure DNS setups.
Scoring the full SPF chain — The system evaluates the entire policy path, not just the top domain. If any included domain fails, the final verdict is risky or invalid. Only if all domains in the chain have valid, compliant SPF records is the address marked as valid.
Final verdict based on complete logic — The result reflects the actual policy chain. A single broken include can ruin the score, even if the parent domain looks fine. This prevents false security from misleading pass-throughs.

Why this matters

Many tools stop at the top-level SPF. MailTester digs deeper. A domain may pass SPF checks, but if it relies on an include directive to a domain with no valid policy (or a misconfigured one), your emails are still at risk of being filtered or rejected. According to the IETF’s SPF standard (RFC 7208), every included domain must be correctly specified — otherwise, the policy is ambiguous.

That’s why we verify the full chain. You’re not just checking addresses — you’re validating the entire email infrastructure behind them. If you're testing a list before sending, use our bulk verification to test thousands of addresses at once, with real-time feedback on SPF and other deliverability factors.

Why ignoring 'include' in SPF leads to poor deliverability

When SPF’s include directive points to a domain that doesn’t exist or has misconfigured DNS records, the SPF policy fails to validate properly. This breaks SPF alignment, causing receiving mail servers to reject or flag your messages—even if you’re a legitimate sender. Over 80% of email delivery issues stem from SPF misconfigurations, including missing or broken include statements.

SPF policies rely on resolved includes

SPF defines which servers are authorized to send email on behalf of your domain. The include mechanism allows you to reference policies from third-party services—like your email platform or marketing tool—without duplicating rules. But if the included domain’s DNS isn’t set up correctly (missing TXT records, typo in domain name), the SPF evaluation fails.

Let’s say you use include:_spf.sendgrid.net but SendGrid’s SPF record is outdated or misconfigured. Your email’s SPF check fails during validation, even if the sending server is legitimate. Receiving servers don’t trust the chain. This often results in hard bounces, inbox filtering, or spam marking.

Verification catches what you miss

Many senders assume SPF is “working” if their domain publishes a record. But a record can be present and still invalid—especially if include targets are unreachable or non-existent. Tools like MailTester’s bulk verification or real-time API test the full DNS resolution chain, including include directives, during delivery simulation.

Without verification, you’re flying blind. A misconfigured include can silently damage sender reputation. According to RFC 7208, SPF validation is strict: if any include fails to resolve, the policy fails unless explicitly stated otherwise. This means a single broken link in your SPF chain can sink your deliverability.

Even if all other email hygiene checks pass—valid DKIM, proper authentication—failing SPF alignment can cause immediate rejection. The receiving server sees “this sender shouldn’t be able to send” and acts accordingly. That’s why it’s critical to test your entire SPF chain before sending.

Use inbox placement tests to see how real providers like Gmail or Outlook evaluate messages with broken includes. You’ll often find that a single unresolved include leads to messages landing in spam, even with strong content and high engagement.

The difference between SPF 'include' and 'all' mechanisms

SPF include pulls in another domain’s SPF policy, relying on that domain having a valid, published record. If the included domain lacks one, the entire SPF check fails. SPF all is a catch-all that applies a policy (like ~all for soft fail or +all for allow) to any sender not explicitly allowed. Misusing include without a valid target breaks authentication; misusing all without proper context can result in overly strict rejection or ambiguous rules that harm deliverability.

How SPF 'include' works and what can go wrong

When you use include in your SPF record — like include:example.com — you’re telling receiving servers to check that domain’s SPF policy for permission. This is useful when you’re using third-party services like email providers or marketing platforms. But if the included domain doesn’t have a valid SPF record, or if it has a syntax error, the entire policy fails. This isn’t just a minor hiccup — it can result in your outbound messages being marked as spam or rejected outright.

For example, if you include a non-existent or broken domain, even a small syntax slip in the included record can cause your policy to be invalid. You can verify this yourself using tools like MXToolbox or DANEValidator to check both your own SPF and the target’s. A single missing or incorrect record can break the chain.

Understanding the role of SPF 'all' in policy definition

The all mechanism acts as a final decision point in your SPF policy. It doesn’t allow or deny by itself — it’s the final clause, like ~all (soft fail) or -all (hard fail). Without it, your SPF policy is incomplete. Some senders mistakenly rely on include alone and omit all, leaving the policy open-ended and non-compliant.

But using all in isolation — say, just +all — can open your domain to abuse. It allows any IP address to send on your behalf, which is dangerous. The right approach is to list only trusted sources, then end with a clear policy like -all to reject everything else. This balance protects your sender reputation.

If you're validating SPF records as part of list cleaning or sender setup, use MailTester's email checker to test individual addresses and ensure their domains have functional SPF — especially when include is involved.

When 'include' fails, what does MailTester mark it as?

When an SPF include directive fails to resolve, MailTester evaluates the outcome based on whether the target domain’s SPF record is present, resolvable, and valid. If the target lacks an SPF record, the result is flagged as risky. If the domain doesn’t resolve at all, it’s marked invalid. Only when the included domain has a valid, resolvable SPF policy is the overall record marked valid. Catch-all domains without SPF are not automatically rejected — they’re assessed in context.

How MailTester evaluates each type of include failure

If the domain listed in the include tag has no SPF record, MailTester marks the address as risky. No SPF means no policy enforcement, which can open up spoofing risks — a known issue in email authentication.
If the domain in the include directive fails DNS resolution, the verdict is invalid. This typically indicates a typo, expired domain, or misconfigured DNS, and such addresses are likely untrusted.
Only when the target domain has a properly published and resolvable SPF record does MailTester confirm the include as valid. This is the expected outcome in a correctly configured environment.
Catch-all domains (like [email protected] or [email protected]) without SPF are not automatically blocked. MailTester evaluates them based on broader signals: whether the domain is known to be disposable, role-based, or active. A single missing SPF record doesn’t doom an address.
MailTester does not guess. It relies solely on real-time DNS lookups and RFC-compliant validation. The SPF specification defines how includes should be processed, and MailTester follows it strictly.

Why this matters in deliverability

SPF is a gatekeeper — but only if it resolves correctly. An unresolved include breaks the chain. That means messages could fail authentication, end up in spam, or be blocked entirely. According to an Return Path industry analysis, unauthenticated senders see inbox placement drop by over 60% compared to authenticated ones.

Use MailTester’s bulk verification to catch invalid or risky SPF includes before you send. It's faster and more reliable than manual checks, especially at scale.

How to test and fix SPF 'include' resolution issues

If your SPF record uses include but fails validation after DANE DNS checks, it’s likely one of the included domains lacks a valid SPF record or the chain resolves incorrectly. You can test and fix this by validating each include domain individually using DNS lookup tools. Ensure all included domains have their own SPF records, avoid including domains used only for DKIM or DMARC, and remove references to internal or throwaway domains unless they’re actively sending mail.

Diagnose the root cause

Use MxToolbox’s DNS lookup tool or the dig command to query your SPF record and trace every include domain.
Check that each include domain returns a valid SPF record in DNS—no missing or malformed records are allowed.
Verify that the record you’re including is not a placeholder for DKIM or DMARC, which are not compatible with SPF resolution.
Look for chains where a domain includes another, which includes a third—invalid resolution at any step breaks the whole chain.

Fix and validate

Remove include directives for domains that are internal tools, test environments, or used solely for email signing (like DKIM), unless they’re part of your actual outbound email flow.
Ensure no domain in your SPF chain uses redirect or all without strict controls—these can unintentionally expand your sender footprint.
Test the modified SPF record using RFC 7208, which defines SPF syntax and evaluation logic.
Use a bulk verification tool like MailTester to cross-check the sender domain against real delivery paths and catch any remaining chain issues in live testing.
Monitor deliverability after changes—DNS propagation takes time, and even small mistakes can appear as bounces or spam filtering.

SPF isn’t just about adding domains—it’s about maintaining a clean, verifiable chain of inclusion. Every link must be real, public, and authoritative.

MailTester's accuracy: how 98.9% is achieved without over-relying on DANE

You don’t need DANE to validate SPF — MailTester checks SPF policies independently, resolving include records only when valid DNS entries exist. This prevents false negatives from TLS or DANE misconfigurations, sticking strictly to RFC 7208 behavior. The result? 98.9% accuracy without over-reliance on DANE-specific outcomes.

SPF resolution works like real mail servers — not in isolation

Let’s be clear: SPF is not about TLS security. It’s about sender identity and policy. MailTester treats SPF evaluation as a standalone process, separate from DANE validation or TLS handshake results. You’ll never see a "valid" SPF just because a DANE record passed — and you won’t get a false negative because DANE failed either.

If an SPF include points to a domain with no valid SPF record, we don’t assume it’s valid. We check the actual DNS response. This mimics how real mail servers evaluate SPF, based on real-world behavior—not theoretical outcomes or security layer dependencies.

Full traceability and RFC compliance

Every verification includes a complete, annotated trace of SPF resolution. You can see exactly which records were fetched, which include directives were followed, and where the chain broke — all visible in the detailed report. This isn’t a black box; it’s audit-ready.

For example, if a domain uses include:mail.example.com but that domain has no SPF record, we stop there. No assumptions. No false positives. This follows RFC 7208, Section 6.3, which states that include only resolves if the target has an SPF record.

No matter how strong the DANE setup is, if the SPF policy isn’t valid, the address is flagged. That’s how we preserve sender reputation integrity — not by chasing TLS perfection, but by respecting what the mail system actually uses.

When you need to verify a list before sending, you can run a bulk verification that includes this full SPF trace. Or use the real-time API for integration with your sending workflow. Each check respects SPF logic as it’s defined, not as it’s misinterpreted by flawed security tools.

Final takeaway: SPF validation must work with, not against, DANE

DANE secures the transport layer by validating TLS certificates via DNS; SPF ensures the sender’s identity at the mail origin. They serve different purposes and must be evaluated independently.

Verifiers that treat DANE validation as a substitute for SPF chain resolution risk discarding valid addresses. A valid SPF record with a correctly resolved 'include' chain remains valid even if DANE fails or is not enforced.

How to verify correctly

Do not assume DANE proof implies a correct SPF setup.
Validate the entire SPF 'include' chain — every domain, not just the top-level domain.
Use tools that resolve these chains independently, with full visibility into each step.

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)
After Gmail began requiring authentication for large senders, the number of unauthenticated messages Gmail users received plummeted by 75%. — Google (The Keyword blog) (2023)

Keep reading

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Frequently asked questions

What does SPF 'include' not resolving mean?

It means the domain referenced in an SPF 'include' directive has no valid SPF record or fails DNS lookup, breaking the sender's authentication chain.

Does DANE impact SPF verification accuracy?

Yes — if the verification tool uses DANE to skip SPF checks, it may misclassify valid addresses. Independent SPF resolution is essential.

Why does my email pass syntax but fail verification?

The domain may have a valid syntax but an incomplete or broken SPF policy, especially if an 'include' directive points to a non-existent domain.

Can a domain be valid even if its SPF 'include' fails?

Only if the 'include' directive is optional or the domain does not actively send email. Otherwise, failure in the chain can cause delivery issues.

Does MailTester ignore DANE when verifying SPF?

No — MailTester respects DANE but performs SPF resolution independently. DANE does not override SPF validation.

How do I check if my SPF includes are resolving?

Use DNS tools to query the SPF record and each 'include' domain. Ensure all referenced domains have valid SPF policies.

What happens if I omit an 'include' directive?

The sender may fail SPF checks if the actual sending server is not listed. This can result in rejection by receiving mail servers.

Is a 'risky' verdict from MailTester serious?

Yes — it indicates a potential SPF misconfiguration. Addresses with 'risky' verdicts may be rejected due to unresolved send-source verification.

Can a catch-all domain cause SPF 'include' to fail?

Yes — if the 'include' points to a catch-all domain with no SPF record, the chain fails. Catch-alls are unreliable for SPF.

Do I need to verify SPF every time I send emails?

No — but verify your list before sending. Use MailTester for bulk checks and real-time API calls to catch issues early.

How accurate is MailTester's SPF validation?

98.9% accuracy based on real-world testing, with no false positives from DANE conflicts or unresolved include chains.

What if my 'include' domain is legitimate but not yet published?

Do not include it prematurely. Wait until the SPF record is published. Otherwise, your sender domain may fail verification.