Why Is DMARC Failing? Causes, Fixes, and How to Verify It

Why is DMARC failing on your domain? In almost every case, it comes down to one of two things: SPF or DKIM isn’t aligned with your visible From address, or a third-party sender hasn’t been authorized yet.. This guide covers both, plus how to tell whether recent Google, Yahoo, or Microsoft enforcement changes are the real reason behind your DMARC failures, and how to verify a failure yourself before you start making changes.

Why Is DMARC Failing? The Short Answer

DMARC is failing when neither SPF nor DKIM authenticates the message and aligns with the visible From domain. To pass, DMARC requires either SPF or DKIM to pass domain alignment. When neither is aligned, this automatically triggers a DMARC failure. In some cases, when a domain is configured with only SPF or DKIM along with DMARC (and not both), DMARC will fail when the SPF/DKIM alignment fails for that message, even if authentication passes.

What Does DMARC Failure Mean?

DMARC failure occurs when an email fails to pass the DMARC check itself. This happens when neither SPF nor DKIM can verify, in an aligned way, that the email is legitimately sent from your domain. “Verify” and “align” are doing separate jobs here, and mixing them up is where most confusion starts.

SPF Can Pass and DMARC Can Still Fail – Here’s Why

Say your marketing platform sends emails using its own return-path domain, mail.esp-provider.com. SPF checks that domain and passes; the sending IP is authorized to send on behalf of mail.esp-provider.com. But your visible From address is yourdomain.com. DMARC doesn’t just check whether SPF passed somewhere, it checks whether the domain that passed SPF matches the visible From domain. mail.esp-provider.com doesn’t match yourdomain.com. So SPF passed, but DMARC still fails.

The same logic applies to DKIM. A message can carry a valid, cryptographically verified DKIM signature, but if the d= domain in that signature (the signing domain) doesn’t match your visible From domain, DMARC treats it as unaligned and the check fails, even though the signature itself is perfectly valid. This is the most common source of the “SPF and DKIM both say pass” confusion, and that’s why alignment, not just authentication, is the first thing to check.

Common Causes of DMARC Failure

Most DMARC failures trace back to a misconfiguration somewhere in your sending infrastructure rather than an actual attack. Here’s a breakdown on how SPF and DKIM failures affect DMARC:

1. SPF Fail

SPF fails for a handful of specific, well-documented reasons:

• Exceeding the 10 DNS-lookup limit: SPF caps out at 10 DNS lookups per check. Once a domain sends through multiple platforms (say, a CRM, an email marketing tool, and internal mail servers) each with its own include mechanism, that limit gets hit fast. When exceeded, SPF fails outright, often with no obvious warning until mail starts bouncing.
• A missing include for a sending service: If you add a new sending platform and forget to add its SPF include, mail from that platform will fail SPF every time.
• Multiple SPF records on one domain: DNS only allows one SPF record per domain. If two exist, most receiving servers can’t determine which to trust and will fail the check.
• Syntax errors: Extra spaces, malformed mechanisms, or an incorrectly ordered record can invalidate the whole thing.

Lear more about why SPF Fails.

2. DKIM Fail

DKIM failures usually come down to one of three things:

• Expired or rotated keys that were never updated in DNS: DKIM keys aren’t permanent. If a key is rotated on the sending side but the new public key isn’t published to DNS, every signature validates against the wrong key and fails.
• A missing or incorrect selector: The selector tells receiving servers which DNS record holds the public key for a given signature. When you get the selector wrong, DKIM verification fails even if the key itself is fine.
• Signatures invalidated after the message is modified post-signing: DKIM signs specific headers and body content. If anything covered by that signature changes after signing, the signature breaks.

You can see our guide on how to set up DKIM and our deeper breakdown of why DKIM fails for troubleshooting specific DKIM failure scenarios and errors.

3. Third-Party Senders Not Authorized (CRMs, ESPs, Helpdesks)

Many businesses send mail through marketing automation tools, CRMs, helpdesk software, and transactional email services. If those platforms aren’t properly authorized to send on behalf of your domain, every message they send might trigger a DMARC fail.

For example, Google Workspace and Microsoft 365 both sign outgoing mail with their own default DKIM selector unless you configure a custom one. That means mail sent through them can show up labeled “via provider.com” to recipients. These messages can fail alignment, since the signing domain doesn’t match your visible From domain, unless you’ve explicitly set up custom DKIM signing for your own domain within that platform.

4. Email Forwarding and Mailing Lists

When an email is forwarded, the forwarding server’s IP isn’t in the original sender’s SPF record, which breaks SPF alignment. The “envelope from” address or headers can also get modified in the process.

Mailing lists are related but not the same. They often modify the message body or headers directly, adding an unsubscribe footer or rewriting the subject line, which breaks the DKIM signature even in situations where forwarding alone wouldn’t. ARC (Authenticated Received Chain) exists specifically to mitigate this by letting intermediate servers attach a verifiable record of the original authentication results. However, it may soon be deprecated with its capabilities being retrofitted into the upcoming DKIM2 specification.

5. Subdomain Misalignment

If your DMARC policy covers yourdomain.com, but emails are sent from mail.yourdomain.com without its own alignment, those emails can fail DMARC checks. Organizations running mail across multiple subdomains need consistent authentication across all of them, not just the root domain.

6. DNS Propagation Delays (Intermittent Failures)

If a DNS record was just changed, some receiving servers may still be looking at the old, cached version, while others have already picked up the new one. That mismatch causes DMARC to pass for some recipients and fail for others at the exact same time, which is a genuinely confusing pattern if you don’t know propagation delay is the cause. If you’ve recently edited an SPF, DKIM, or DMARC record and failures look inconsistent rather than universal, give it time (often up to 24-48 hours, depending on the record’s TTL) before assuming something else is wrong.

Check your DNS propagation live https://powerdmarc.com/dns-propagation-checker/

7. Domain Spoofing (DMARC Working as Intended)

If someone is impersonating your domain to send phishing or spam emails, those messages will naturally fail DMARC, since the unauthorized source doesn’t pass SPF or DKIM checks aligned to your domain. This is the one cause on this list that isn’t a misconfiguration. It’s DMARC doing exactly what it’s designed to do, and it’s a signal your domain is being actively targeted, and it’s worth monitoring closely in your DMARC reports.

8. Seeing a Specific Bounce Message or Error Code?

If you landed here searching for a specific error string, all of the following are just DMARC or alignment failures surfaced in each platform’s own language. The underlying causes and fixes are everything covered above.

Mimecast’s “DNS Authentication: DMARC Fail”

This is Mimecast’s own way of flagging that an inbound or outbound message failed DMARC evaluation, typically for the same SPF/DKIM alignment reasons described above.

SendGrid delivery errors

Errors referencing DMARC usually mean SendGrid’s own sending domain, or a customer’s From domain sent through SendGrid, isn’t properly aligned, often because a custom DKIM/SPF setup for the sending domain hasn’t been completed.

Gmail’s SMTP codes

421-4.7.26 is a temporary error, meaning the message is unauthenticated (no aligned SPF or DKIM pass), and Gmail has been escalating these to permanent 550-5.7.26 rejections more aggressively for persistent non-compliance since late 2025. A related code, 550-5.7.1, specifically means the message failed under the sending domain’s own published DMARC policy.

Microsoft’s 550 5.7.515

This is a hard rejection Microsoft introduced for high-volume senders (5,000+ emails/day to Outlook, Hotmail, or Live.com addresses) that don’t meet its authentication requirements, effective from May 5, 2025.

Why Did DMARC Suddenly Start Failing?

If your domain was passing DMARC and recently started failing, run through this list before assuming something is broken:

• A new marketing tool, CRM, or helpdesk platform was added without updating your SPF or DKIM setup.
• A DNS record was recently edited and now has a syntax error or an accidental duplicate SPF record.
• A DKIM key was rotated or expired without the new key being published to DNS.
• A subdomain started sending mail without its own SPF, DKIM, or DMARC alignment.
• Google, Yahoo, or Microsoft tightened enforcement on their end.

Google, Yahoo & Microsoft Are Enforcing DMARC More Strictly Than Ever

Google and Yahoo’s bulk-sender requirements were announced in late 2023 and took effect for high-volume senders in February 2024, with full enforcement following by April 2024. Since then, Gmail has continued tightening how aggressively it converts temporary deferrals into permanent rejections for domains that remain non-compliant, a pattern that’s become noticeably stricter through late 2025.

Microsoft followed with its own requirements for Outlook, Hotmail, and Live.com addresses. Enforcement started on May 5, 2025 with non-compliant bulk mail (5,000+ emails/day) being now rejected outright with the error 550 5.7.515, rather than simply routed to spam.

If your domain sends 5,000 or more emails a day to any of these providers and DMARC has started failing more often recently, this enforcement tightening, may well be why. The fix is the same either way: find every sending source, get SPF and DKIM properly aligned, and confirm your DMARC record is correct. For the full requirements by provider, see our bulk email sender requirements guide.

How to Verify a DMARC Failure

Before making changes, confirm what’s actually happening:

1. Send a test message to Gmail, Outlook, and Yahoo, then open the Authentication-Results header.

In Gmail, open the message and select “Show original.” In Outlook, use “View Message Details.” Look for spf=, dkim=, and dmarc= results, and check whether the passing domain matches your visible From address.

2. Cross-reference the failing source IP against your DMARC aggregate (RUA) reports.

These reports show every IP sending mail on behalf of your domain and whether each one passed or failed, which is usually the fastest way to spot an unauthorized or misconfigured source. You can see our guide on how to read DMARC reports if the raw XML format is unfamiliar.

3. Run the domain through a free DMARC Checker

Confirm the current state of your records, since a record that looked correct when it was published can develop syntax issues, duplicates, or propagation gaps over time. Our DMARC record checker covers this in one pass.

What Happens When DMARC Fails?

The outcome depends entirely on the DMARC policy set for your domain. Your policy tells receiving mail servers how to handle emails that don’t pass authentication, and each level carries different consequences.

p=none: Monitoring only

With a DMARC policy set to p=none, emails that fail DMARC are still delivered, but they frequently land in the spam folder rather than the inbox. This policy is designed for monitoring. It allows you to collect DMARC reports and identify authentication issues without disrupting your email flow. While it’s a safe starting point, keeping p=none long-term leaves your domain vulnerable since it doesn’t actively block unauthorized senders.

p=quarantine: Sent to spam

Under a DMARC policy of p=quarantine, failed emails are sent to the recipient’s spam folder. This reduces visibility and user engagement because your legitimate emails may end up buried alongside junk mail. While this policy offers more protection than p=none, it can still hurt your business if legitimate emails are failing due to misconfigurations rather than actual spoofing.

p=reject: Blocked entirely

A DMARC policy of p=reject will result in receiving servers completely blocking the email, preventing it from reaching the recipient at all. This is the strictest and most secure policy. It stops phishing and spoofing attempts dead in their tracks. However, if your SPF and DKIM aren’t properly configured, a p=reject policy will also block your own legitimate emails, which can severely disrupt business communications.

Impact of DMARC Failures on Your Business

DMARC failures pose significant challenges for businesses that depend on email for communication. Here’s how a DMARC fail can impact your organization.

Reduced email deliverability

DMARC failures can result in legitimate emails being blocked or rejected by inbox providers, impacting business communications. Whether your emails land in spam or get rejected entirely, the result is the same: your messages aren’t reaching the people who need to see them. For businesses that rely on email for sales, marketing, customer support, or transactional communications, this directly translates to lost opportunities.

Damaged sender reputation

Repeated DMARC failures can harm your domain’s sender reputation, making it harder for even authenticated emails to reach the inbox. Mailbox providers like Google and Microsoft track your domain’s authentication history. When they see a pattern of DMARC failures, they begin treating your domain as less trustworthy, which means even properly configured emails may start facing deliverability issues over time.

Lower open rates and customer engagement

DMARC failures can lead to emails being sent to spam folders, reducing open rates and customer engagement. If your marketing campaigns, invoices, order confirmations, or important business updates are consistently landing in spam, your audience simply won’t see them, leading to missed revenue and frustrated customers.

Increased phishing and spoofing risk

A high DMARC fail rate increases the risk of phishing attacks and domain spoofing, eroding customer trust. If your domain is being spoofed, unauthorized sources will fail DMARC checks, but without a strict enforcement policy, those spoofed emails may still reach recipients, putting your customers, partners, and employees at risk of falling for fraudulent messages sent under your brand’s name.

Long-term deliverability damage

DMARC failures can signal to mailbox providers that a domain isn’t trustworthy, which can have long-term implications for email deliverability. Rebuilding a damaged sender reputation takes significant time and effort. Once authentication is back in order, gradually rebuilding inbox trust through structured IP warmup, increasing outbound volume in measured daily increments and generating positive engagement signals from real recipients, is often what determines how quickly deliverability actually recovers.

How to Fix a DMARC Fail

Fixing a DMARC fail requires understanding why the failure occurred and making the right adjustments to your email authentication setup.

Step 1: Start with a relaxed DMARC policy (p=none)

With a none policy, you can begin by monitoring your domain with DMARC (RUA) Aggregate Reports and keeping a close eye on inbound and outbound email, which helps you respond to delivery issues before they escalate.
This allows legitimate messages to keep reaching recipients even if DMARC fails for them, though it does leave you vulnerable to phishing and spoofing in the meantime.

Step 2: Ensure Proper SPF and DKIM Alignment

Check your DNS record for errors, and confirm that the domain passing SPF or DKIM actually matches your visible From address, the exact mechanism explained earlier in this guide. Our free DMARC checker tool can catch errors in your DMARC syntax or DNS record formatting, including extra spaces and spelling mistakes.

Using both DKIM and SPF together provides a layered approach: DKIM verifies the message hasn’t been tampered with, while SPF verifies the sending server’s identity. Together, they help establish trust in the email’s source and reduce the risk of spoofing and unauthorized email activity.

Step 3: Strengthen Your Defense with Enforcement

Once legitimate senders are confirmed and aligned, shift to an enforced policy (p=quarantine, then p=reject) to gain real protection against domain spoofing and phishing attacks.

Step 4: Protect with AI-Driven Threat Detection

Take down malicious IP addresses and report them directly from your DMARC platform to prevent future impersonation attempts, using threat intelligence tooling where available.

Step 5: Continuously Optimize with Failure Reports

Enable DMARC (RUF) Failure reports to get detailed information about specific cases where emails failed DMARC, so you can trace the root of the problem and fix it faster.

Fix DMARC Failure With PowerDMARC

Dealing with DMARC failures can be complex, especially when you’re managing multiple sending services, third-party platforms, and evolving email infrastructure. PowerDMARC simplifies the entire process, from initial setup to ongoing monitoring and threat detection.

We help organizations correctly deploy DMARC by providing step-by-step guidance and automation tools that ensure your DMARC records, SPF, and DKIM authentication are properly configured and aligned from day one. This reduces the risk of misconfigurations that lead to DMARC failures and gets your domain on the path to full enforcement faster.

Once DMARC is in place, PowerDMARC continuously monitors your email traffic and generates real-time reports and alerts whenever a DMARC fail is detected.

Here’s what makes us unique:

• AI-driven threat intelligence and automated alerts that identify phishing and spoofing attempts in real time
• Step-by-step onboarding and implementation support to get DMARC, SPF, and DKIM right from day one
• Human-readable, actionable reporting that replaces complex XML data with clear insights
• Trusted by 5,000+ organizations worldwide to fix and prevent DMARC failures

Frequently Asked Questions

1. What does DMARC stand for?

DMARC stands for Domain-Based Message Authentication, Reporting, and Conformance. It’s an email authentication protocol that helps protect domains from email spoofing, phishing, and other cyber attacks by verifying that emails are legitimately sent from authorized sources.

2. How to pass DMARC authentication?

To pass DMARC authentication, your emails must pass either SPF or DKIM and align with the domain shown in the “From” address. To make this happen, ensure your sending IPs are authorized in SPF, DKIM is properly signed, and your DMARC record is correctly published in DNS.

3. How to fix no DMARC protection?

To fix the lack of DMARC protection, publish a DMARC record in your domain’s DNS. Start with a monitoring policy (p=none) to collect reports, then gradually move to stronger enforcement (p=quarantine or p=reject) once you’ve confirmed all legitimate email sources are authenticated.

4. How to fix the DMARC fail error?

To fix the DMARC fail error, start by checking why the message failed authentication. Make sure SPF and DKIM are correctly set up and aligned with the sending domain, then verify your domain’s DMARC policy is published correctly in DNS and matches how your emails are actually sent. Once everything is aligned, monitor DMARC reports to confirm the issue is resolved.

5. What is a DMARC violation?

A DMARC violation is another way of describing a message that fails the DMARC check, either because it’s unauthorized (someone spoofing your domain) or because a legitimate sender isn’t properly aligned. What happens next depends on your policy: p=none logs it, p=quarantine sends it to spam, and p=reject blocks it outright.

6. Can DMARC fail even if SPF and DKIM both pass?

Yes, and this is one of the most common points of confusion. SPF and DKIM can both technically pass their own checks while DMARC still fails, if neither one’s passing domain aligns with your visible From address. A message from mail.esp-provider.com can pass SPF cleanly and still fail DMARC if your visible From domain is yourdomain.com, since alignment, not just authentication, is what DMARC actually checks.

• About
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Maitham Al Lawati

Cybersecurity Expert, CEO at PowerDMARC

Maitham is a tech entrepreneur, cybersecurity expert, CEO and Founder of PowerDMARC with 15+ years of industry experience. Maitham holds a Global MBA from the University of Manchester and various professional certifications including CISSP, CISM, CRISC, and ISC2 CCSP.

Latest posts by Maitham Al Lawati (see all)

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