Why does SPF all=* fail in relayed email flows?

You send a transactional email through a third-party service. It bounces. You check the headers. The error says “SPF all=* authentication failure due to spoofing in relayed email flows.” You’re not a spammer. So why did your email get blocked?

SPF all=* is designed as a safety net—but it backfires when messages pass through relays. It allows any IP to send on behalf of your domain. That’s not a feature. It’s a flaw that attackers exploit. When the email gets relayed, the sending IP changes. SPF checks fail. Legitimate mail gets rejected. But it’s not broken. It’s working as intended.

Key takeaways

  • SPF all=* permits any IP to send mail for your domain, making it unusable in relayed flows
  • Relaying through services like SendGrid or Mailchimp changes the sending IP, breaking SPF validation
  • SPF failures in relayed flows are not errors—they’re deliberate security measures against spoofing

How does SPF all=* expose domains to spoofing?

If your SPF record includes all=*, you're telling every email server on the internet: “Anyone can send mail claiming to be from this domain.” This setting deliberately disables sender authentication, letting attackers relay emails through unauthorized servers using your domain as the From: address. Even if DKIM and DMARC are configured, a misconfigured SPF breaks the alignment chain that protects inbox placement and sender reputation.

Why SPF all=* breaks sender authentication

SPF (Sender Policy Framework) is meant to specify which servers are authorized to send mail for a domain. When you set all=*, you’re not just being permissive—you’re turning off the validation check entirely. Any IP address can now claim legitimacy, regardless of whether it’s yours or not. This is not a configuration mistake; it’s a deliberate flaw that invites abuse.

Let’s be clear: no standard email system trusts a domain with a all=* SPF policy. Reputable receiving servers—like those at Gmail, Microsoft, or Yahoo—automatically flag messages from such domains as high-risk or outright reject them. This isn't hypothetical. The IETF's RFC 7208 (which defines SPF) explicitly warns against over-permissive records, though implementation varies in practice. Section 2.1 of the SPF specification states that failing to include a mechanism means no authorization is implied—so all=* essentially removes accountability.

How attackers exploit permissive SPF records

Attackers know that domains with all=* SPF records are easy targets. They craft emails with forged From: headers—say, [email protected]—and send them through compromised machines or open relays. Since SPF no longer blocks the send, the message passes initial checks. If DKIM is missing or invalidated, the receiving server has nothing to validate alignment against.

Even if your domain has a valid DKIM signature and DMARC policy (like rua=mailto:[email protected]), the attack succeeds because SPF is the first gate. When SPF fails to authenticate, the entire alignment chain breaks. DMARC’s enforcement depends on SPF and DKIM both passing with alignment. If SPF is set to all=*, the DMARC policy becomes irrelevant for that domain, especially if the email is not aligned with the domain.

Reputable providers like Spamhaus (Spamhaus) and MxToolbox track domains with poor SPF configurations. These are commonly listed in abuse databases, especially when used in phishing or spam campaigns. Fixing this doesn’t just improve deliverability—it stops attackers from using your brand as a front.

Use MailTester’s email checker to verify if a single address is valid before sending. For larger lists, use bulk verification to detect and remove invalid or risky addresses before outreach. While SPF errors don’t appear directly in verification results, clean sender infrastructure—including correct SPF records—reduces bounce rates, blocks, and inbox placement issues across all campaigns.

What happens when relayed emails violate SPF policy?

If a relayed email fails SPF validation because the sending IP isn’t listed in the domain’s SPF record, the receiving server will reject it outright or tag it as spam—regardless of whether DKIM or DMARC appear valid. This happens because SPF checks the original sending IP, and if it doesn’t match the allowed sources, authentication fails. The result is bounces, poor inbox placement, and long-term damage to sender reputation—even with proper DKIM or DMARC setup.

Why SPF is checked even with DKIM or DMARC

SPF, DKIM, and DMARC are independent checks. A single failure in SPF is enough to break delivery, even if DKIM signs the email correctly or DMARC alignment passes. This is by design: receiving servers treat SPF as the first-line defense against spoofing. The receiving mail server evaluates SPF first, before checking DKIM or DMARC, since SPF is the quickest and most widely implemented check.

When an email is relayed through a third-party service—like a marketing platform, CRM, or proxy server—the original sending IP might not be authorized in the domain’s SPF record. For example, if you send via an email service and your domain uses SPF with a strict all=reject policy, a relayed message from an IP outside that list will fail SPF. This is common with shared hosting, unverified transactional gateways, or misconfigured relay setups.

Consequences of SPF failure in relayed flows

When SPF fails in a relayed email flow, the receiving server typically denies delivery or applies a spam score. According to industry data from Return Path, emails that fail SPF are 42% more likely to land in spam folders or be rejected outright.

This isn’t just a one-time issue. Repeated SPF failures can trigger blocklisting, especially if the domain sends at scale. ISPs track sender reputation over time, and failing SPF consistently reduces deliverability across major providers like Gmail, Outlook, and Yahoo. You can verify SPF issues before sending by checking a domain’s record via tools like MxToolbox or by examining DNS records directly using RFC 7208.

Let’s say you use a tool like MailTester to validate your list before blasting. You can catch invalid, disposable, or non-receiving addresses early, but you still need to ensure your relay setup respects SPF. For real-time verification of email addresses in your workflow, try the MailTester API, which includes SPF checks as part of its broader validation process. If you’re sending at scale through third-party platforms, validate your SPF policy matches your actual sending infrastructure. That’s the only way to avoid unexpected bounces and inbox placement issues.

How do relayed flows break SPF alignment?

When email is relayed through a third-party service—like a CRM, helpdesk, or marketing platform—the message travels from the relay’s IP, not yours. SPF checks the sending IP against your domain’s static SPF record. If that IP isn’t listed, SPF fails, even if the relay is legitimate. This is a common cause of authentication failures in automated workflows and transactional messaging.

SPF records are rigid, not adaptive

Your SPF record is a hardcoded list of IPs authorized to send on your behalf. It doesn’t update when you add a new service. If you use a third-party SMTP provider for emails triggered by customer actions—say, a new order or support ticket—those messages come from the provider’s IP, not yours. If that IP isn’t in your SPF record, the receiving server sees it as spoofing, even if the content is clean and the sender is real.

Let’s say you send transactional emails via SendGrid, which uses a pool of IP addresses. Even if your domain’s SPF record includes SendGrid’s range, some IPs in that pool may drift in and out of your authorized list due to load balancing. Without real-time validation, some messages will fail SPF by default. This is especially true when your SPF record uses include mechanisms with third-party providers whose IP ranges change dynamically.

Relayed flows amplify the problem

Automated systems aren’t built to handle email authentication quirks. When a CRM forwards a message to a customer via a relay, it may strip or alter headers, making alignment with your SPF record harder to prove. Even if the relay is trustworthy, the IP mismatch breaks SPF—especially in environments where DMARC policies are set to reject messages (policy=reject).

Many marketers assume SPF is “done” once they configure it. But in practice, it breaks whenever the sending infrastructure changes. The result? High bounce rates, delivery failures, or messages marked as spam. According to the RFC 7208 (the standard governing SPF), SPF must be evaluated from the point of initial delivery—meaning the first hop in the chain must match the sender’s SPF record, not a downstream relay.

You can’t catch every relayed IP failure with static SPF alone. Monitoring and validating sender IP alignment in real time is crucial. Tools like MailTester’s email verification API help you identify risky or invalid inboxes before sending, reducing the chance of spoofing flags and maintaining sender reputation.

For teams relying on third-party services, combining SPF with DKIM and DMARC is better than relying on SPF alone. But even then, the relay layer remains a weak point unless the IP is explicitly authorized. Use tools that test your sending infrastructure’s alignment—not just your list quality—to keep your deliverability intact.

What are the real risks of using SPF all=*?

Using SPF all=* is a security anti-pattern that grants blanket permission to any server to send email on your domain’s behalf, making it trivial for malicious actors to spoof your address. This policy undermines email authentication, increases the risk of impersonation, and leads to higher bounce rates and reduced inbox placement—especially with providers like Gmail and Outlook, who now actively penalize overly permissive SPF records.

It invites abuse and impersonation

SPF all=* means any mail server can claim to represent your domain. That includes attackers setting up fake mail relays to send phishing or spam campaigns that appear to come from your organization. The result? Your domain gets associated with abuse, even if you didn’t send the email.

Mail servers like Gmail and Outlook now detect and flag overly permissive policies like this. According to an industry-standard practice reported by the Messaging, Malware, and Mobile Anti-Abuse Working Group (M3AAWG), overly broad SPF policies are commonly seen as a red flag in email verification and sender reputation assessments.

It breaks DMARC enforcement

DMARC relies on consistent SPF and DKIM results to enforce policies like quarantine or reject. But with SPF all=*, the authentication result is unpredictable. An email might pass SPF if sent through a permitted server, and fail if sent through a relay that’s not listed—but the outcome doesn’t reflect your actual sending behavior.

When SPF is unreliable, DMARC cannot be enforced with confidence. That means even if you set up a DMARC policy to reject unauthenticated mail, it won’t reliably block spoofed messages. Your domain remains vulnerable, and your legitimate emails are more likely to land in spam folders.

Many organizations that have used SPF all=* report noticeable drops in inbox placement—sometimes over 15-20%—and higher bounce rates due to domain reputation damage. In some cases, entire domains get labeled as high-risk by blacklists like Spamhaus.

If you're sending email at scale, use SPF responsibly. Only list servers you control. Test your setup with tools like the MailTester email checker or the inbox placement tester before sending to your list. That way, you catch invalid or risky addresses early, reducing the chance that a flawed SPF record harms your sender reputation.

How to fix SPF all=* issues in relayed flows

SPF all=* is a common cause of authentication failures in relayed email flows because it explicitly permits any IP to send on your domain’s behalf, which violates SPF’s core purpose: preventing spoofing. Remove all=* immediately and instead authorize only the specific IPs or services—like SendGrid or Mailchimp—that legitimately send email for you. Use include: statements to safely reference third-party SPF records, and test your updated configuration with tools like MxToolbox or MailTester’s DNS lookup to verify it works.

Step-by-step correction

  1. Remove all=* from your SPF record. It’s never required for legitimate sending. Allowing any IP to send on your behalf creates an open relay, making your domain vulnerable to abuse. This violates SPF’s foundational design and triggers spam filters.
  2. Add only authorized senders. List the specific IPs or domain names of services that send emails on your behalf, such as your ESP or marketing platform. Be precise—each IP or domain must be explicitly permitted.
  3. Use include: to reference trusted third-party SPF records. If you use SendGrid, Mailchimp, or another provider, add a line like include:sendgrid.net instead of listing their IPs directly. This maintains accuracy and reduces configuration errors.
  4. Test your SPF configuration. Use public DNS tools like MxToolbox or the MailTester API to verify your SPF record resolves correctly and doesn’t allow untrusted IPs. Run checks frequently after changes.
  5. Ensure every relayed IP is explicitly authorized. If you’re relaying through another system—like a customer service platform or internal relay—verify those IPs are in your SPF record. A single unauthorized IP can break authentication and trigger delivery failures.

Why trust matters

SPF isn’t just about technical correctness—it’s about proving you’re not spoofing. When your SPF record allows anyone to send on your domain’s behalf, email providers treat that as a sign of poor sender hygiene. According to RFC 7208, SPF is designed to "limit the ability of unauthorized sources to send mail on behalf of a domain," not to grant global permission. Misconfigured SPF undermines your sender reputation and increases the risk of being blocked or flagged as spam.

Always validate your SPF record after changes. Tools like MailTester’s inbox placement testing let you simulate delivery across real inboxes, identifying issues before you send. If you’re verifying large lists, use bulk email verification to catch suspicious addresses early and keep your sender reputation clean.

What SPF records should you actually use?

Use a minimal, precise SPF record: spf1 include:_spf.your-provider.com -all. Avoid all=* or all=~—they allow unauthorized senders to spoof your domain. Use -all only during testing. Never combine multiple mechanisms without understanding their interactions. Recheck your SPF record every time you add a new email service.

Stick to the essentials

  • Use spf1 include:_spf.your-provider.com -all as your base record. This includes only trusted sending sources and rejects all others.
  • Never use all=*—it means “anyone can send as your domain.” This is the opposite of secure.
  • Avoid all=~ (soft fail) in production. It allows spoofed messages to bypass filters and can be exploited by abuse.
  • Use -all only temporarily during configuration validation—once proven stable, ensure it’s not used in high-volume or critical flows.
  • Don’t combine mechanisms like include, ip4, and mx unless every component is verified and aligned. Overcomplication leads to errors and unintended opens.

Keep your SPF record current

Every time you add a new sender, email platform, or third-party tool (like a CRM or marketing system), audit your SPF record immediately. Too many includes exceed the 10-lookup limit defined in RFC 7208, which can cause your SPF to fail silently.

For example, if you use Mailchimp, SendGrid, and HubSpot, each will require its own include directive. Mismanagement here can break deliverability.

Use a tool like MailTester’s bulk verification tool to check whether your email list includes addresses that might trigger SPF failures or appear in spoofed messages. It helps isolate invalid or risky addresses before they impact sender reputation.

For real-time checking, especially when debugging, use MailTester’s email checker to verify individual addresses for validity, including SPF-aligned delivery readiness.

SPF is not a standalone fix. It works best when paired with DMARC and DKIM—part of a layered authentication strategy.

For a fuller picture of how SPF fits into the bigger deliverability picture, see the RFC 7208 specification. It details the expected behavior of SPF implementations, including the importance of strict policy enforcement via -all.

Always test changes in a low-traffic environment first. A single misconfigured SPF record can lead to widespread email delivery failures. When in doubt, start simple, then add trusted components one at a time.

Can DMARC protect you if SPF fails due to relayed sending?

If your SPF record includes all=* and you're relaying emails through a third-party service, SPF will fail — and DMARC cannot stop that failure. DMARC only acts when SPF or DKIM pass with alignment. Without alignment, DMARC enforcement is meaningless. Even with a strict policy=reject in DMARC, your email will be blocked if SPF fails due to relayed IP mismatches.

Why SPF failure breaks DMARC

DMARC requires either SPF or DKIM to pass with alignment. If SPF fails — say, because the sending IP isn't authorized in the domain's SPF record — DMARC has no authority to enforce policy. It simply cannot act on a failed check. You can set DMARC to reject all non-compliant messages, but if SPF fails, there's nothing DMARC can do to fix it.

Let’s say your domain’s SPF record says include:thirdparty.com, but the relayed email comes from an IP not listed in that include. The SPF check fails. Now, even if DKIM passes, DMARC doesn’t care — it checks for alignment, and if SPF fails, the whole chain collapses.

How relayed sending breaks SPF

When you send via a relayed service — like a marketing platform, a CRM, or a transactional email provider — the sending IP changes. That IP must be explicitly allowed in your SPF record. If it isn’t, and you've set all=*, it still doesn’t help: all=* only allows the IPs listed in the SPF policy, not any arbitrary one.

Many domains use all=* in SPF to simplify things, but this is a misconfiguration. It doesn’t authorize relays. It only allows the IPs listed. Without proper inclusion, SPF fails. And once SPF fails, DMARC cannot protect you.

Even with a strong DMARC policy, a misconfigured SPF record — especially one relying on all=* without proper mechanisms — means your emails are at risk of being rejected. This is not a flaw in DMARC — it’s a flaw in the SPF setup.

It’s possible to test for these issues. Use an email verification tool to check if an address is valid, deliverable, and not a catch-all. A tool like MailTester’s email checker can identify issues with invalid or non-deliverable addresses before you send. For broader testing, inbox placement testing can expose how your messages appear in recipients’ inboxes, including whether they’re marked as spam.

How to test SPF compliance before sending at scale

You can test SPF compliance by verifying sender domains with tools like MailTester, checking real IP addresses against SPF records before use, running inbox-placement tests to simulate actual delivery, and auditing your entire list for domains with weak or missing SPF configurations. This proactive validation prevents authentication failures and reduces bounce rates before you send at scale.

Validate your sender infrastructure early

  • Use MailTester’s email checker to validate individual addresses and confirm their domains have properly configured SPF records before adding them to a campaign.
  • Run SPF checks on every sending IP address via a tool that parses DNS records—you can use MailTester’s real-time verification API to automate this across your IP portfolio.
  • Check for spf=all policies or overly permissive mechanisms like spf:include to external domains, which increase spoofing risk and may indicate misconfiguration.

Test real-world delivery conditions

  • Use MailTester’s inbox-placement tester to send test emails to major inboxes and observe how SPF, DKIM, and DMARC policies are enforced in practice.
  • Audit your full email list with MailTester’s bulk verification to detect domains with missing, weak, or misconfigured SPF policies across your entire database.
  • Monitor your bounce logs and feedback loops weekly—early detection of authentication failures helps you adjust SPF records or remove problematic domains before they harm sender reputation.

SPF failures in relayed email flows often stem from relaxed policies like spf=all or untrusted third-party includes. Tools like MailTester don’t just report failure—they help you distinguish between genuine issues and false positives. The SPF specification (RFC 7208) states that only authorized hosts should be listed in an SPF record, making strict validation essential. Let’s treat SPF like a firewall: not just a check, but a gatekeeper.

SPF records with all=* or overly permissive mechanisms let anyone relay emails on your behalf, making your domain a spoofing target. MailTester catches these flaws during bulk list verification, stopping weak authentication from dragging down your sender reputation before a single email goes out. By blocking high-risk addresses early, you avoid delivery failures and keep your IP and domain standing in good stead with inbox providers.

Spotting Permissive SPF Before It Breaks Your Inbox Placement

When SPF uses all=*, it essentially says “anyone can send emails pretending to be from me.” That’s a red flag to mail filters. MailTester checks each domain in your list against this pattern during verification, flagging addresses tied to domains with overly relaxed SPF policies. It’s not just about validity—it’s about whether the email infrastructure behind the address can be trusted.

Many deliverability issues trace back to sender authentication, not content or lists. The industry-standard practice—enforced at scale by providers like Google and Microsoft—is to reject or demote mail from domains with broken SPF, DKIM, or DMARC alignment. By catching these flaws before you send, you’re not just cleaning up your list; you’re hardening your overall send reputation. For context, RFC 7208 (which defines SPF) discourages the use of all=* for the exact reason it opens your domain to abuse.

Verification That Fits Into Your Workflow

Let’s be clear: you don’t want to verify every address manually. That’s why MailTester integrates with tools you already use—SendGrid, Mailchimp, Klaviyo—so real-time checks happen at the moment you’re about to send. If an email address points to a domain with a problematic SPF setting, it gets flagged before the campaign fires.

Even during list hygiene, the in-app AI assistant helps you catch SPF misconfigurations without deep technical knowledge. It doesn’t just say “invalid”—it explains why the address might fail delivery, often pointing to SPF, DMARC, or catch-all issues behind the scene. This level of insight is rare in bulk tools.

And because your purchased credits never expire, you can verify lists continuously without urgency or waste. Long-term deliverability health isn’t about one-time fixes—it’s about consistent scrutiny. That’s why MailTester works at scale, not just in bursts.

Learn how verification works in practice: check your entire list for SPF, role accounts, and delivery risks with a single upload.

Final takeaway: SPF all=* is not a solution—it’s a vulnerability

SPF all=* allows any sender to claim legitimacy, effectively removing sender authentication from the equation. This creates a direct path for spoofing in relayed email flows, where abuse can go undetected.

Relayed emails require precise SPF records—specific, audited, and enforced—not broad, permissive policies. A single flawed record can compromise sender reputation across all messages sent through that chain.

Proactive verification with tools like MailTester identifies invalid, catch-all, or spoofable addresses before they impact deliverability. Testing inbox placement and authentication alignment ensures that policies are not just correct in theory, but effective in practice.

Good deliverability starts with accurate SPF policy enforcement. Sender authentication isn’t about alignment alone—it’s about precision, consistency, and trust. The right tools catch flaws before they cause bounces, blocklists, or lost engagement.

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Frequently asked questions

What does SPF all=* mean in a DNS record?

SPF all=* allows any IP address to send email on behalf of the domain, disabling sender authentication. It’s a severe security risk.

Can SPF all=* cause an email to be marked as spam?

Yes. Receiving servers detect overly permissive SPF policies as signs of potential spoofing and may reject or mark the email as spam.

How do relayed email services affect SPF validation?

Relay services use their own IP addresses. If that IP isn’t listed in the domain’s SPF record, authentication fails.

Does DMARC protect against SPF failures?

No. DMARC depends on SPF and DKIM passing. If SPF fails, DMARC will not enforce policies like quarantine or reject.

How can I check if my domain uses SPF all=*?

Use DNS lookup tools or MailTester’s real-time API to analyze your domain’s SPF record for permissive policies.

Should I use SPF all=* when testing email delivery?

No. Test with properly configured SPF records to simulate real-world sender conditions. Use all=~ (soft fail) only temporarily.

What happens if I remove SPF all=* without adding authorized IPs?

Emails from unlisted IPs will fail SPF validation, leading to bounces and potential reputation damage. Always authorize legitimate senders.

It detects flawed SPF configurations during bulk verification and flags risky domains. Its 98.9% accuracy helps prevent sending to invalid or insecure recipients.

Are SPF records case-sensitive?

No. SPF records are not case-sensitive, but the formatting and syntax must follow DNS standards precisely.

Can I have multiple SPF records for one domain?

No. Multiple SPF records cause DNS errors and can result in failed authentication. Use a single, properly formatted SPF record with multiple mechanisms.

How often should I audit my SPF configuration?

Audit at least quarterly or whenever you add a new email sender, service, or integration to ensure only authorized IPs are included.

Can a catch-all email account cause SPF failure?

Catch-all accounts don’t directly cause SPF failure, but they expose domains to abuse. Combined with weak SPF, they increase spoofing risks.