DMARC Fail Explained: Causes, Fixes, and Troubleshooting Guide

One of the most common email authentication problems businesses face is DMARC failure. If your emails are failing DMARC checks, mailbox providers may:

• Send your emails to spam
• Quarantine your messages
• Reject emails completely

DMARC failures can seriously impact:

• Email deliverability
• Cold email campaigns
• Marketing performance
• Brand reputation

The good news is that most DMARC issues are fixable once you understand what causes them.

In this guide, you’ll learn:

• What DMARC fail means
• Common DMARC failure causes
• SPF and DKIM alignment problems
• How to fix DMARC failures
• Best practices for monitoring and prevention

You can also quickly test your domain using the LeadCanal Domain Scanner, which checks:

• SPF
• DKIM
• DMARC
• Authentication health

For individual testing, you can also use:

• SPF Checker
• DKIM Checker
• DMARC Checker

What Does DMARC Fail Mean?

DMARC failure happens when an email does not properly pass SPF or DKIM authentication and alignment requirements.

DMARC is designed to help mailbox providers verify:

• The sender is legitimate
• The email was not spoofed
• The domain is authorized

If these checks fail, the receiving server follows the DMARC policy defined in your DNS record.

Depending on your DMARC policy:

• Emails may still be delivered
• Sent to spam
• Rejected completely

How DMARC Authentication Works

To understand DMARC failure, it’s important to understand how DMARC validates emails.

DMARC relies on two authentication methods:

• SPF
• DKIM

For DMARC to pass:

• SPF OR DKIM must pass authentication
• AND alignment must pass

This is where many businesses encounter problems.

SPF Alignment Failures

SPF alignment is one of the most common reasons for DMARC failure

SPF checks

• Whether the sending server is authorized

DMARC then checks:

• Whether the SPF-authenticated domain matches the visible “From” domain

If those domains do not align, DMARC may fail even if SPF technically passes

Example of SPF Alignment Failure

Visible sender:

support@example.com

SPF Return-Path:

mailer.thirdparty.com

In this example:

• SPF may authenticate successfully
• But alignment fails because the domains differ

This often happens with:

• CRM systems
• Newsletter tools
• Marketing platforms
• Cold email software

How to Fix SPF Alignment Issues

To fix SPF alignment:

• Configure custom return-path domains
• Use branded tracking domains
• Authenticate third-party providers properly

Many providers like:

• Mailchimp
• SendGrid
• HubSpot

support domain alignment customization.

DKIM Alignment Failures

DKIM alignment problems are another major cause of DMARC failure

DKIM verifies

• The authenticity of the message signature

DMARC then checks:

• Whether the DKIM signing domain matches the visible sender domain

If the domains differ:

• DKIM alignment fails
• DMARC may fail

Example of DKIM Alignment Failure

Visible sender:

sales@example.com

DKIM signing domain:

mail.vendor.com

In this case:

• DKIM authentication may pass
• But alignment fails because the domains are different

How to Fix DKIM Alignment Issues

Common fixes include:

• Enabling custom DKIM signing
• Using your own domain for signing
• Configuring domain authentication inside third-party platforms

Always ensure:

• The visible sender domain
• The DKIM signing domain

align properly.

Common Causes of DMARC Failure

DMARC failures usually happen because of configuration issues rather than server outages.

Missing SPF Records

If no SPF record exists:

• SPF authentication fails
• DMARC may fail

You can verify SPF using the LeadCanal SPF Checker

Missing DKIM Configuration

If DKIM is not enabled

• Message signatures are missing
• DKIM fails

This is very common with:

• New domains
• Third-party senders
• Misconfigured mail systems

Incorrect DNS Records

DNS mistakes often break authentication.

Common errors include:

• Wrong selectors
• Incorrect TXT formatting
• Missing semicolons
• Invalid tags

You can validate records using the LeadCanal Domain Scanner.

Third-Party Sending Platforms

Many businesses forget to authenticate:

• CRM systems
• Email marketing tools
• SaaS applications
• Cold email platforms

This causes:

• SPF failures
• DKIM failures
• Alignment issues

Every sending platform must be authenticated correctly.

Email Forwarding

Forwarding can break SPF authentication because:

• The forwarding server is not listed in SPF

This is why DKIM is extremely important since DKIM signatures often survive forwarding.

How to Read DMARC Reports

DMARC reports provide visibility into:

• Who is sending emails from your domain
• Authentication failures
• Alignment issues
• Suspicious activity

These reports are usually sent in XML format.

Aggregate Reports (RUA)

Aggregate reports summarize:

• SPF pass/fail rates
• DKIM pass/fail rates
• Sending IP addresses
• Authentication statistics

Example DMARC tag:

rua=mailto:dmarc@example.com

These reports help identify:

• Unauthorized senders
• Misconfigured services
• Deliverability problems

Forensic Reports (RUF)

Forensic reports provide:

• Detailed failure information
• Individual failed message samples

Example:

ruf=mailto:forensics@example.com

Not all mailbox providers send forensic reports due to privacy policies.

How to Fix DMARC Failures

Fixing DMARC failures usually involves improving authentication and alignment.

Step 1: Verify SPF

Check:

• SPF syntax
• Authorized senders
• Lookup count
• Missing providers

Use:

• LeadCanal SPF Checker

Step 2 : Verify DKIM

Check:

• DKIM signatures
• DNS records
• Selectors
• Domain alignment

Use:

• LeadCanal DKIM Checker

Step 3 : Verify DMARC

Check:

• Policy syntax
• Alignment configuration
• Reporting addresses

Use:

• LeadCanal DMARC Checker

Or analyze everything together with the:

• LeadCanal Domain Scanner

Step 4 : Authenticate Every Sender

Every platform sending emails for your domain must be authenticated.

This includes:

• Marketing tools
• CRM systems
• Helpdesk platforms
• Cold email software
• Transactional email providers

Many DMARC failures happen because businesses forget one provider.

v=DMARC1; p=none;