SPF Include Loop in AWS SES

Why is your AWS SES email delivery failing due to SPF?

You’re sending emails through AWS SES, your logs show no bounces, no complaints—yet recipients aren’t seeing your messages. You’re not blacklisted, your sender reputation looks fine. What’s really happening?

The issue might not be in your content or list hygiene. It could be a silent policy rejection caused by an SPF include loop. When SPF records chain through multiple domains in a recursive loop, receiving servers reject the email without warning. This breaks inbox placement without a trace, gradually damaging your sender reputation.

SPF include loops are a hidden but common cause of email delivery failure in AWS SES. They trigger policy-level rejections that don’t generate bounce messages, making them particularly hard to detect. Understanding how these loops work—and how to fix them—is critical to maintaining consistent deliverability.

Key takeaways

SPF include loops cause silent policy rejections in AWS SES, resulting in undetected delivery failures.
These loops occur when SPF records reference each other recursively, violating the SPF specification’s limit on include chain depth.
Fixing the loop requires auditing and simplifying your SPF record to avoid repeated or nested domain references.

What is an SPF include loop, and how does it affect AWS SES?

An SPF include loop happens when two or more domains reference each other in their SPF records—like domain A includes domain B, and domain B includes domain A—creating a circular dependency. AWS SES rejects emails from domains with such loops, even if the rest of the SPF syntax is correct, because the policy cannot be evaluated. This causes immediate rejection, often resulting in hard bounces or silent drops before delivery.

How SPF Loops Form in Practice

You might set up SPF records to trust multiple domains, like your marketing and internal systems. If example.com includes mail.example.net, and mail.example.net includes example.com, you’ve created a loop. Though this seems harmless, SPF evaluation limits recursion to prevent infinite checks. Once the limit is hit, the policy is deemed invalid.

According to RFC 7208, SPF records are checked for logical consistency and recursion depth. When loops exceed the allowed depth, the policy fails. AWS SES strictly follows these standards, so a loop—even if syntactically correct—triggers immediate rejection during email submission.

Why AWS SES Enforces This Rigidly

SPF is a core part of email authentication. AWS SES validates the full SPF policy before accepting an email. If there’s ambiguity or a loop, it can’t verify whether a server is authorized, so it treats the entire message as untrusted. This prevents abuse but can break legitimate workflows.

Even if your email passes other checks—like DKIM or DMARC—SPF failure in SES stops delivery. You’ll often see a hard bounce with a message like “550 5.7.1 SPF check failed” or simply no bounce at all, leading to lost messages and reduced sender reputation.

Common sources of loops include third-party email services that don’t account for existing domain inclusions or misconfigured DNS by overzealous admin teams. Tools like MailTester's bulk verification help detect such issues early by checking for common SPF misconfigurations, including loops.

Always validate SPF records using tools based on actual RFC standards—like the official SPF specification or DNS lookup services. Never assume that a simple “syntax OK” check is enough.

How to detect SPF include loops in your domain configuration

You can detect SPF include loops by validating your SPF record with tools like MxToolbox or the AWS SES console, manually inspecting for recursive 'include' directives, and tracing inclusion chains to catch circular dependencies—such as Domain A including Domain B, which in turn includes Domain A—before deployment.

Use tools to validate SPF records

Run your SPF record through MxToolbox’s SPF Checker to identify syntax errors, overly long records, or known loops in the chain.
Check the AWS SES console under "Identity Management" to view SPF validation results for domains you’re using with SES; it will flag policies rejected due to loop issues.
Monitor for the explicit error: "SPF policy rejected due to include loop" — this is a standard response from AWS SES when a recursive include is detected.

Trace inclusion chains manually and automatically

Look for include: directives that point to domains you don’t control or that may indirectly include your domain—especially if those domains themselves use includes that reference back to you.
Check for circular references: if Domain A includes Domain B, and Domain B includes Domain A, a loop forms. This can happen even across multiple levels of includes.
Use automated tools to trace the full inclusion chain, such as the MailTester bulk verification tool, which can help you pre-validate sender records across domains with real-time diagnostics.
Before deploying new SPF records, simulate the full chain using a tool that resolves includes recursively—this catches issues you’d otherwise miss during manual review.

SPF records must not exceed 10 DNS lookups—exceeding this limit triggers a temporary failure, even if the loop isn’t immediately visible.

The SPF specification limits DNS lookups to reduce load and prevent infinite loops. Each include: counts as a lookup, so even a small loop can push you over the 10-look-up threshold.

Real-world example: SPF include loop causing AWS SES policy rejection

You're getting SPF policy rejection from AWS SES not because your email is spammy, but because your SPF record creates a loop: mycompany.com includes client.com, which includes mycompany.com, and so on. This recursive chain exceeds AWS’s safe recursion limit—typically 10 levels—and triggers a policy rejection during validation, even if the rest of the setup is technically sound.

The loop in action

Check your SPF record for any include: statements. In this case: v=spf1 include:client.com include:vendor.com -all. It looks fine at first glance—you’re trusting two domains.
Check the included domains’ records. client.com has v=spf1 include:mycompany.com -all. vendor.com mirrors that: v=spf1 include:mycompany.com -all. Now, the loop is clear.
Trace the recursion chain: mycompany.com → client.com → mycompany.com → client.com → ... This chain continues until it hits AWS SES’s limit. Even if the total includes don’t exceed 10, the recursion depth itself is what gets blocked.
Recognize the root cause: SPF validation is recursive. Each include: expands to another record. If records point back to each other, the process can run infinitely in theory. AWS SES limits recursion to prevent denial-of-service attacks via malformed SPF records.
Fix the loop by removing one of the include statements that causes the cycle. If client.com and vendor.com are legitimate partners, use include: safely—only if they don’t reference your domain. Otherwise, use ip4: or include: with non-circular sources.

Why AWS SES blocks this

AWS SES enforces strict SPF validation to maintain email integrity. According to the IETF’s SPF spec (RFC 7208), implementations must limit recursion depth to avoid infinite loops. While the standard doesn’t specify an exact number, AWS’s behavior aligns with this principle. You can verify this in your AWS SES console when you get a rejection message like “SPF policy is invalid” or “Too many include lookups.”

The 5 steps described in “The loop in action”, in order.

If you're unsure whether your SPF setup is valid, use a real-time SPF validator like MxToolbox to trace the chain. Or, check your domain’s record with RFC 7208 as a reference for the spec that underlies these rules.

You don’t need to guess. Run your domain’s SPF through a tool that checks for loops and validity. With MailTester’s bulk verification, you can validate multiple domains' SPF and DMARC records at scale, catch loops early, and avoid send failures before they happen. For automated checks, use the verification API to integrate SPF checks into your workflow. If you're managing outbound email, inbox placement testing helps confirm your deliverability once the SPF is fixed.

How to validate SPF records properly before sending with AWS SES

You can prevent SPF policy rejections in AWS SES by validating your SPF record using the AWS console or CLI tools, avoiding multiple include directives unless you control all referenced domains, limiting includes to non-cyclic providers like SendGrid or AWS SES, and verifying no include loops exist via DNS tracing. Always test before sending to avoid delivery failures.

Check SPF status in AWS SES

Use the AWS SES console to check the current SPF validation status for your domain under Identity Management.
Run aws sesv2 get-identity-policies via the CLI to verify policy configuration and SPF alignment.
Confirm your domain’s SPF record passes the SPF syntax check using a tool like MXToolbox or RFC 7208 standards.

Prevent include loops and invalid configurations

Never use multiple include directives unless you fully control every domain referenced in the chain.
Limit includes to trusted, non-cyclic providers such as include:_spf.sendgrid.net or include:amazonses.com.
If using third-party includes, trace the full DNS chain using dig TXT or Google’s DNS lookup to detect loops back to your own domain.
Replace complex includes with specific ip4: or ip6: records when possible to reduce reliance on external policies.
If your domain appears in a chain that loops back to itself (e.g., include:example.com where example.com includes your domain), revise the record immediately—this invalidates SPF and causes rejection.
Use a service like MailTester’s bulk verification to check sender reputation and domain alignment across a list before sending at scale.

SPF loops cause policy rejections even if the record is syntactically valid—prevention is simpler than fixing deliverability issues after they occur.

Let’s be honest: a single misconfigured include can break outbound deliverability across thousands of emails. You don’t need to solve every edge case manually—tools like MailTester’s real-time API (API Email Checker) can help validate sender domains before they hit the wire.

Alternatives to using 'include' that prevent looping

Instead of relying on include mechanisms that can cause SPF policy rejection in AWS SES, use direct ip4 or ip6 entries for your sending IPs, or flatten your SPF record by combining all allowed IPs into a single, no-include record. Avoid chains of includes, especially across domains you don’t control. This eliminates the risk of looping and reduces policy evaluation complexity. You can verify your SPF setup with tools like MxToolbox or Spf-reporting.com, both trusted by deliverability experts.

Prefer direct IP-based mechanisms

When you know the exact IP addresses your email is being sent from, use ip4:192.0.2.0/24 or ip6:2001:db8::/32 in your SPF record. These are unambiguous and don’t introduce third-party dependencies. If you’re using AWS SES, your sending IPs are known and stable—especially if you’re using dedicated IPs. Direct IP entries avoid the chain of DNS lookups that can trigger a policy loop during evaluation.

Limit includes to fully controlled domains

If you must use include, only do so for domains you own and monitor closely. Including domains you don’t control introduces fragility—any change in their SPF record can break your own. Even small edits, like adding a new sender or removing a service, can invalidate your entire policy. If you’re managing multiple services, consider whether you can consolidate their sending IPs into one SPF record to eliminate include dependencies entirely.

Reduce dependency on SPF with DMARC and DKIM

SPF is not the only gatekeeper. Proper DMARC alignment with DKIM and SPF allows you to maintain deliverability even if SPF fails. If DKIM passes and the domain aligns with the header from domain, DMARC will pass—meaning your email may still deliver. This lets you relax strict SPF requirements. Use DMARC alignment strategies to reduce the need for complex SPF chains.

Flatten SPF for multi-domain setups

In multi-domain or multi-service environments, avoid chaining includes across domains. Instead, gather all valid sending IPs into one authoritative SPF record on a single domain. Apply a single include only if that domain is your primary sending source. This SPF flattening approach simplifies DNS lookups and prevents infinite evaluation loops. Tools like MailTester’s bulk verification can help you audit your list’s sending IPs before finalizing your SPF strategy.

You can catch SPF include loops and malformed policies before they block your emails. MailTester’s inbox placement tests validate sender infrastructure in real time, uncovering configuration flaws like recursive SPF includes that trigger rejection in AWS SES. This stops bounces before they happen.

Real-time detection of SPF policy flaws

When you send through AWS SES, SPF policies must be strictly compliant. Any include loop—like include:example.com that itself includes include:yourdomain.com—can cause policy rejection. MailTester checks these during inbox placement testing, simulating real-world gateways and flagging loops or excessive includes. It’s not just about syntax; it’s about alignment with standards like RFC 7208, which defines how SPF should be processed.

The tool doesn’t stop at catching errors. It runs these checks across your full list of sender addresses, identifying problematic domains in bulk. That means if one of your partners uses a domain with a broken SPF chain, you’ll know before you send to it. This is critical in environments where multiple third-party senders share infrastructure.

Proactive alerts and AI-assisted fixes

MailTester’s bulk verification feature scans thousands of addresses at once, surfacing infrastructure risks like SPF loops. It’s not just a black-or-white validation—it identifies risky configurations and ranks them by severity. This transparency lets you prioritize fixes that impact deliverability most.

When a loop is detected, the in-app AI assistant suggests paths to simplify your SPF record. It doesn’t rewrite your policy—but it can propose removing redundant includes, flattening nested chains, or splitting policies where needed. This guidance is backed by industry-standard practices: according to RFC 7208, SPF policies must be no more than 10 include mechanisms to avoid processing failures.

Deliverability reports include SPF health metrics: count of include mechanisms, recursive checks, and domain chain depth. These help you track changes over time and ensure compliance before scaling sends. Use the inbox placement tester to validate your domain’s full sender stack, or the bulk verification tool to audit your list for infrastructure risks.

Let's be clear: SPF loops aren’t just a technical hiccup. They break authentication and get flagged as spam-like behavior. Fixing them early—using tools that check not just syntax but path structure—is how you maintain sender reputation.

SPF best practices for AWS SES users

SPF policy rejections in AWS SES often stem from a recursive include chain, where one domain's SPF record references another that includes back to the first. This looping breaks SPF validation and leads to email rejection. To avoid it, keep your SPF record simple—under 10 mechanisms and 10 includes—and only include domains you control or fully trust. Always validate the full chain using DNS lookup tools.

Core SPF configuration rules

Use no more than 10 mechanisms in your SPF record (e.g., include, a, mx, ip4, ip6).
Limit the number of include directives to fewer than 10 to avoid chain length issues.
Only include domains you own or have explicit written permission from the owner to use.
Never create a recursive include path—verify each domain in the chain using standard DNS tools like MXToolbox or dnsper.net.
Prefer using include:spf.protection.outlook.com only if you’re certain it doesn’t create a loop with your own domain’s record.

Monitor and validate SPF/DKIM alignment

Deploy DMARC with a policy of none or quarantine initially to collect alignment reports.
Use DMARC’s rua tag to send aggregate reports to a monitoring mailbox—this reveals missing authentication or alignment failures.
Inspect report details to spot misconfigured SPF or DKIM failures, especially when using third-party services like AWS SES.
Align SPF checks with your sending domain. If sending from mail.company.com, ensure SPF alignment is configured for that subdomain.
Regularly test your sender reputation and deliverability using tools like MailTester’s inbox placement checker to catch issues before they impact outreach.

SPF is not about blocking spam—it’s about verifying the identity of sending domains. When configured wrong, it blocks legitimate email.

Use your real-time email verification API to catch invalid or poorly configured addresses before they reach AWS SES. Combined with bulk list verification at MailTester, you can reduce bounce rates and improve sender reputation. AWS SES itself doesn’t perform address-level validation—but you should.

Finally, if you’re relying on multiple third-party services (e.g., SendGrid, Klaviyo, Salesforce), ensure their SPF records don’t conflict with your own. Use the MailTester integrations with popular platforms to verify list quality and alignment before sending. Your goal is a clean, consistent authentication trail—from the DNS record to the final inbox.

Why SPF errors are hard to catch but critical for deliverability

SPF policy rejections in AWS SES don’t show up as bounces—they’re silent. They still hurt your sender reputation, degrade inbox placement over time, and increase the risk of being blocked, even though they don’t trigger immediate error messages. If you’re sending at scale, these unnoticed failures quietly hurt your deliverability.

They don’t bounce, but they still matter

When AWS SES rejects an email due to an SPF policy violation, it doesn’t return a hard bounce. Instead, the message vanishes without a trace. That makes detection nearly impossible unless you’re actively monitoring SMTP logs or analyzing inbound feedback loops. It’s easy to miss, especially during a campaign audit when you’re only reviewing delivered or bounced emails.

These silent failures degrade sender reputation over time. Each one counts against you, even if you never see it. Mail providers like Gmail and Outlook track these anomalies, and consistent SPF policy violations can eventually lead to your IP or domain being flagged, even if no one gets a bounce notification.

How they hurt your inbox placement

Over time, repeated SPF policy rejections—even if not reported—signal poor email hygiene to filters. High-volume senders can unknowingly trigger threshold-based actions that hurt inbox placement. You might see a slow drop in open rates, not because of content, but because your messages are being treated as suspicious.

SPF includes loops are a common cause of these rejections. If your SPF record references another domain’s record that in turn references back, you create a loop that violates the SPF specification. This isn’t always easy to detect during setup. It’s often only after sending hundreds of thousands of messages that the damage manifests.

Let’s use a real example: A company using AWS SES with multiple third-party senders accidentally added multiple include directives that created a circular reference. Their SPF record was valid in theory, but in practice, the validator stack failed due to recursion limits. This caused silent rejections—no bounces, no alerts—and after six months, their inbox placement dropped 30%.

Tools like MailTester’s inbox placement tester can help identify these issues early by simulating delivery to major inboxes and surfacing policy-level problems before they scale. You can also use the real-time verification API to catch bad records before they go live.

It's not just about avoiding outright failure. It's about protecting your reputation, especially at scale. SPF errors aren’t the kind of bug you can fix in an hour and forget—because they don’t show up, they grow silently. And that’s exactly why they’re so dangerous. For more guidance on SPF setup, refer to the official SPF specification (RFC 7208).

Final step: verify your SPF configuration using real email flows

You must send real emails through AWS SES to actual inboxes on Gmail, Outlook, and Yahoo, then inspect the full headers for SPF 'fail' or 'permerror' results. Only real email flows reveal policy rejections caused by SPF include loops that internal checks miss. Use tools like MailTester’s inbox-placement tester to simulate delivery across providers before sending to your entire list.

Test your SPF setup with real-world delivery

Send test emails via AWS SES to addresses hosted on Gmail, Outlook, and Yahoo. These are the major providers where SPF policy errors commonly trigger delivery failures.
Retrieve the full email headers from the recipient’s inbox (or use a tool like MxToolbox for header inspection). Look for the spf=fail or spf=permerror result in the authentication report.
Confirm the source of the failure by checking whether it's caused by an include loop in your SPF record—such as referencing a domain that itself includes another domain your record already points to. This breaks SPF policy and causes outright rejection.
Validate with end-to-end inbox testing using MailTester’s inbox-placement test. It simulates delivery to real inboxes across providers and flags SPF policy rejections before you send to your full list. This avoids wasting sends and damaging sender reputation. Learn more.

Monitor and maintain your SPF record

SPF records are not set-and-forget. Every time you add a new email service (like a new CRM, marketing tool, or third-party platform), you must add its mechanism to your SPF record. But adding too many mechanisms leads to include loops or exceeding the 10 DNS lookup limit.

Use tools like RFC 7208 to validate the structure of your record. You can also use DNS lookup tools to trace include chains and detect circular references.

Update your record immediately when changes occur. Use MailTester’s bulk verification to check existing senders and detect misconfigurations in your entire list before you send. Verify your list with real-time API checks to catch issues early. And when you scale, integrate with your ESP using our pre-built integrations for better control.

Conclusion: Clean SPF configuration is non-negotiable for AWS SES success

An SPF include loop, though seemingly small, directly triggers policy rejection in the AWS SES email gateway by invalidating the SPF record. Even a single misconfigured include directive can result in rejected messages and degraded sender reputation.

Protecting deliverability means validating SPF records before sending and using tools that test real-world gateway behavior. Real-time verification and inbox testing uncover these issues before they impact campaigns, preserving list hygiene and sender trust.

Fixing SPF is not a one-time task—it's a foundation. A clean SPF record ensures compliance, strengthens authentication, and supports consistent inbox placement across major providers.

Sources

Roughly one in six legitimate commercial emails (16.5%) never reaches the inbox globally — 6.7% is filtered to spam and 9.8% disappears without a bounce. — Validity 2025 Email Deliverability Benchmark Report (2025)
Benchmark testing of 15 major email service providers found about 10.5% of legitimate emails land in the spam folder and a further 6.4% go undelivered. — EmailTooltester deliverability benchmark (via WarmForge) (2026)

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Frequently asked questions

What does SPF policy rejection mean in AWS SES?

It means the sender's domain SPF record contains a syntax or structural error—such as an include loop—that prevents the email from being accepted by the gateway.

Can SPF loops cause permanent email blocking?

Not directly, but repeated rejections due to SPF loops degrade sender reputation and can lead to blocklist placement over time.

How many 'include' directives are allowed in an SPF record?

SPF records are limited to a maximum of 10 mechanisms and include statements; exceeding this causes validation failure.

Does AWS SES validate SPF records before sending?

Yes. AWS SES checks SPF policy validity during email submission. Invalid policies, including loops, result in immediate rejection.

How can I test for SPF loops without a tool?

Trace each 'include' chain manually via DNS lookup tools, ensuring no domain loops back to itself or its parent domain.

Is it safe to use 'include' for third-party services?

Yes, if you control or trust the third-party domain. Never include domains whose SPF records you cannot audit.

Can DKIM or DMARC fix an SPF loop?

No. DKIM and DMARC do not replace SPF, and a loop in the SPF record still causes rejection regardless of other headers.

How often should I audit my SPF record?

At least quarterly, and after adding any new email-sending service to your domain's infrastructure.

What happens if I ignore an SPF include loop?

Emails will be silently rejected by AWS SES, reduce sender reputation, and hurt long-term delivery rates.

Can MailTester detect SPF include loops?

Yes—MailTester’s deliverability testing and API include checks that flag risky configurations, including SPF loops, in real-time.