# Fix DNS DMARC Authentication Fail

Your emails are failing DMARC authentication, or you're seeing errors like "DNS authentication DMARC fail" or "rua / ruf domains not valid" when setting up DMARC. DMARC (Domain-based Message Authentication, Reporting, and Conformance) is critical for email deliverability and preventing spoofing.

Introduction

This article covers troubleshooting steps and solutions for Fix DNS DMARC Authentication Fail. The error typically occurs in production environments and can cause service disruptions if not addressed promptly.

Symptoms

Common error messages include:

```bash # Query DMARC record dig TXT _dmarc.yourdomain.com +short

# Or using nslookup nslookup -type=TXT _dmarc.yourdomain.com

# Check with Google's DNS dig TXT _dmarc.yourdomain.com @8.8.8.8 +short ```

bash
dig TXT yourdomain.com +short
bash
# Find DKIM selector (usually in email headers)
dig TXT default._domainkey.yourdomain.com +short

Common Causes

  • Configuration misconfiguration
  • Missing or incorrect credentials
  • Network connectivity issues
  • Version compatibility problems
  • Resource exhaustion or limits
  • Permission or access denied

Understanding DMARC

DMARC tells email receivers how to handle messages that fail SPF or DKIM checks. It consists of a DNS TXT record at _dmarc.yourdomain.com.

Step-by-Step Fix

Check existing DMARC record:

```bash # Query DMARC record dig TXT _dmarc.yourdomain.com +short

# Or using nslookup nslookup -type=TXT _dmarc.yourdomain.com

# Check with Google's DNS dig TXT _dmarc.yourdomain.com @8.8.8.8 +short ```

Verify SPF record:

bash
dig TXT yourdomain.com +short

Verify DKIM record:

bash
# Find DKIM selector (usually in email headers)
dig TXT default._domainkey.yourdomain.com +short

Test DMARC with online tools:

```bash # Use MXToolbox curl -s "https://mxtoolbox.com/api/v1/dmarc/yourdomain.com"

# Or dmarcian curl -s "https://dmarcian.com/dmarc-inspector/yourdomain.com" ```

Common Errors and Solutions

Error 1: DMARC Record Not Found

bash
# Error: No DMARC record found
dig TXT _dmarc.yourdomain.com
# (empty response)

Solution: Create a DMARC TXT record:

```dns # Basic DMARC record (monitoring mode) _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com"

# Strict DMARC record (quarantine) _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=quarantine; pct=100; rua=mailto:dmarc@yourdomain.com"

# Strict DMARC record (reject) _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=reject; pct=100; rua=mailto:dmarc@yourdomain.com; ruf=mailto:dmarc-fail@yourdomain.com" ```

Error 2: rua/ruf Domains Not Valid

bash
# Error: DNS DMARC rua / ruf domains not valid
# The reporting domain must be verified

Cause: External reporting domains require explicit authorization.

Solution: If using an external domain for reports, add a verification record:

dns
# If rua points to external domain (e.g., dmarc-reports@reports.example.com)
# Add verification record at reports.example.com
yourdomain.com._report._dmarc.reports.example.com. IN TXT "v=DMARC1"

For self-hosted reports:

dns
# Use your own domain for reports
_dmarc.yourdomain.com. IN TXT "v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com"

Error 3: DMARC Fails Despite Valid SPF/DKIM

bash
# SPF passes, DKIM passes, but DMARC fails

Cause: Alignment mismatch - the domain in the From header must match the domain used for SPF/DKIM.

Solution: Check alignment settings:

```dns # Strict alignment (exact match required) _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=reject; aspf=s; adkim=s"

# Relaxed alignment (subdomains allowed) _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=reject; aspf=r; adkim=r" ```

Verify alignment in email headers:

```bash # Check From header domain From: user@subdomain.yourdomain.com

# For strict alignment, SPF/DKIM must be for subdomain.yourdomain.com # For relaxed alignment, SPF/DKIM can be for yourdomain.com ```

Error 4: SPF Not Configured

DMARC requires SPF to pass:

dns
# Add SPF TXT record at domain root
yourdomain.com. IN TXT "v=spf1 include:_spf.google.com include:sendgrid.net ~all"

Verify SPF:

bash
dig TXT yourdomain.com +short
# Should return SPF record starting with "v=spf1"

Error 5: DKIM Not Configured

DMARC requires DKIM to pass:

```bash # Generate DKIM keys (example for Postfix) opendkim-genkey -D /etc/opendkim/keys/yourdomain.com -s default -d yourdomain.com

# The generated default.txt contains the DNS record cat /etc/opendkim/keys/yourdomain.com/default.txt ```

Add DKIM record to DNS:

dns
default._domainkey.yourdomain.com. IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC..."

Error 6: Multiple DMARC Records

bash
# Error: Multiple DMARC records found
dig TXT _dmarc.yourdomain.com +short
# Returns multiple records

Solution: Remove duplicate records, keep only one:

```bash # Check for duplicates dig TXT _dmarc.yourdomain.com +short | wc -l

# Should return 1 ```

Error 7: Subdomain DMARC

For subdomains, create separate DMARC records:

```dns # Main domain _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=reject; rua=mailto:dmarc@yourdomain.com"

# Subdomain (optional, inherits from parent if not set) _dmarc.subdomain.yourdomain.com. IN TXT "v=DMARC1; p=reject; rua=mailto:dmarc@yourdomain.com"

# Or use sp tag for subdomain policy _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=reject; sp=reject; rua=mailto:dmarc@yourdomain.com" ```

Error 8: DMARC Reports Not Received

bash
# rua/ruf configured but no reports received

Solution: Check report email configuration:

```bash # Verify rua email exists dig MX yourdomain.com +short

# Test email delivery echo "Test" | mail -s "DMARC Test" dmarc-reports@yourdomain.com

# Check mail logs tail -f /var/log/mail.log ```

Error 9: Percent Policy Too Low

dns
# pct=1 means only 1% of failing emails are affected
_dmarc.yourdomain.com. IN TXT "v=DMARC1; p=reject; pct=1"

Solution: Gradually increase pct as you verify everything works:

```dns # Start with monitoring _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=none; pct=100"

# After 1-2 weeks, quarantine 25% _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=quarantine; pct=25"

# After another week, quarantine 100% _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=quarantine; pct=100"

# Finally, reject 100% _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=reject; pct=100" ```

DMARC Record Components

TagDescriptionExample
vProtocol versionv=DMARC1
pPolicy (none/quarantine/reject)p=reject
spSubdomain policysp=reject
pctPercentage affectedpct=100
ruaAggregate report URIrua=mailto:dmarc@example.com
rufFailure report URIruf=mailto:dmarc-fail@example.com
aspfSPF alignment (s/r)aspf=r
adkimDKIM alignment (s/r)adkim=r
riReport interval (seconds)ri=86400
foFailure reporting optionsfo=1

Verification

After configuring DMARC:

```bash # Verify DMARC record dig TXT _dmarc.yourdomain.com +short

# Check SPF dig TXT yourdomain.com +short

# Check DKIM dig TXT default._domainkey.yourdomain.com +short

# Test with online validator # https://dmarcian.com/dmarc-inspector/ # https://mxtoolbox.com/dmarc.aspx ```

Send test email and check headers:

bash
# Look for Authentication-Results header
Authentication-Results: mx.google.com;
   spf=pass (google.com: domain of user@yourdomain.com designates 1.2.3.4 as permitted sender) smtp.mailfrom=user@yourdomain.com;
   dkim=pass header.i=@yourdomain.com;
   dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=yourdomain.com

Complete DMARC Setup Example

DNS Records

```dns # SPF yourdomain.com. IN TXT "v=spf1 ip4:1.2.3.4 include:_spf.google.com ~all"

# DKIM default._domainkey.yourdomain.com. IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3..."

# DMARC (start with monitoring) _dmarc.yourdomain.com. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:dmarc-reports@yourdomain.com; ruf=mailto:dmarc-fail@yourdomain.com; ri=86400; aspf=r; adkim=r" ```

Processing DMARC Reports

```bash # Install dmarc parser pip install parsedmarc

# Parse incoming reports parsedmarc --output /var/log/dmarc-reports/ /var/mail/dmarc/

# Or use dmarc-report-analyzer npm install -g dmarc-report-analyzer ```

Monitoring Dashboard

```bash # Use dmarcian or similar service # https://dmarcian.com/

# Or self-hosted with Grafana # https://github.com/domainaware/parsedmarc ```

Prevention

  1. 1.[ ] DMARC TXT record exists at _dmarc.yourdomain.com
  2. 2.[ ] SPF TXT record exists at yourdomain.com
  3. 3.[ ] DKIM TXT record exists at selector._domainkey.yourdomain.com
  4. 4.[ ] rua/ruf email addresses are valid and receiving
  5. 5.[ ] External rua/ruf domains have verification records
  6. 6.[ ] Only one DMARC record exists
  7. 7.[ ] Alignment settings match your email configuration
  8. 8.[ ] pct value is appropriate for your rollout stage
  9. 9.[ ] Test emails pass DMARC authentication
  10. 10.[ ] Reports are being received and processed
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