How to handle DMARC forensic reports?

Understanding DMARC Forensic Reports

DMARC forensic reports (RUA and RUF aggregate and forensic reports) provide detailed insights into authentication failures, potential abuse, and legitimate mail flow problems. While aggregate reports show high-level statistics, forensic reports contain actual message samples that failed authentication, enabling detailed analysis of email security issues.

Properly interpreting and acting on forensic report data helps organizations identify and fix email infrastructure problems, detect spoofing attacks, and improve overall email security posture.

Types of DMARC Reports

Aggregate Reports (RUA)

Aggregate reports summarize authentication results:

• Daily summaries grouped by sending domain and IP
• High-level pass/fail statistics
• No actual message content
• Generally safe to share

Forensic Reports (RUF)

Forensic reports contain specific message samples:

• Individual messages that failed authentication
• DKIM/SPF failure reasons
• Message headers and partial content
• May contain sensitive information
• Useful for troubleshooting and abuse investigation

Setting Report Preferences

v=DMARC1; p=reject; rua=mailto:[email protected]; ruf=mailto:[email protected]; fo=1

• rua: Email address for aggregate reports
• ruf: Email address for forensic reports
• fo=0: Send forensic reports only for DMARC failures
• fo=1: Send forensic reports for all failures

Interpreting Forensic Report Data

Report Structure

Forensic reports contain:

• Report metadata (date, sending domain, reporting organization)
• Message headers (From, To, Subject, Date)
• DKIM signatures and verification results
• SPF check results
• DMARC alignment assessment

Understanding Failure Reasons

DKIM Failures:

• Signature not present
• Signature verification failed
• Signature expired
• Invalid signature format

SPF Failures:

• IP not in SPF record
• SPF record malformed
• Too many DNS lookups (SPF max)
• Hard fail policy applied

DMARC Alignment:

• From domain doesn't align with DKIM signature domain
• From domain doesn't align with SPF result domain

Common Forensic Report Scenarios

Scenario 1: Legitimate Mail Infrastructure Issues

Signs:

• Reports show consistent sending IPs
• Known email services (Salesforce, HubSpot, etc.)
• Regular patterns

Response:

1. Identify which service is sending
2. Update DKIM records for that service
3. Add IP to SPF record
4. Verify records with service documentation
5. Monitor forensic reports for improvement

Example:

DKIM failure: HubSpot newsletter sending from IP 123.45.67.89
- Add to SPF: `include:hubspot.com`
- Verify DKIM domain alignment
- Wait 48 hours for DNS propagation
- Monitor next forensic reports

Scenario 2: Potential Phishing/Spoofing

Signs:

• Unknown sender IPs
• No legitimate mail source identified
• Attempting to send as your domain
• Failed DKIM and SPF checks

Response:

1. Document attacker IP addresses
2. Report to abuse contacts
3. Strengthen authentication policies
4. Implement BIMI for visual branding
5. Consider implementing DMARC quarantine/reject

Example:

Forensic report shows emails failing DKIM/SPF from IP 192.0.2.1
- IP not in known services
- Attempting to spoof [email protected]
- No legitimate reason for this mail

Actions:
1. Block IP at firewall level
2. Report to ISP abuse contact
3. Monitor for related IPs
4. Ensure DMARC policy is enforce (p=reject)

Scenario 3: User Device/Misconfiguration

Signs:

• Reports from employee IP ranges
• Clients using older protocols
• Signature mismatches

Response:

1. Contact users about mail client issues
2. Provide correct client configuration
3. Update mobile device policies
4. Ensure proper SMTP authentication

Processing Forensic Reports at Scale

Automated Report Processing

Many organizations receive hundreds of forensic reports daily. Automation helps:

# Parse forensic reports
# Extract sending IPs
# Group by origin
# Alert on suspicious patterns

Creating Forensic Dashboards

Track forensic data over time:

• Percentage of mail passing DKIM/SPF
• Top failure reasons
• Suspicious IPs and origins
• Trends and patterns

This identifies emerging issues early.

Responding to Forensic Reports

Investigation Process

Step 1: Gather Information

• Identify sending domain
• Note sending IP address
• Review failure reason
• Check message content

Step 2: Determine Legitimacy

• Is this a known service? (Check documentation)
• Is this expected mail? (Customer notification? Billing?)
• Is this an authorized system? (Employee tool? Partner service?)

Step 3: Categorize

• Legitimate but misconfigured
• Legitimate but authentication issue
• Malicious/spoofing attempt
• Spam or abuse

Step 4: Take Action

• Fix authentication for legitimate sources
• Block or report malicious sources
• Document resolution steps

Managing Forensic Report Privacy

Sensitive Information Concerns

Forensic reports may contain:

• Usernames and passwords in message headers
• Personal identification information
• Credit card numbers in email content
• Confidential business information

Privacy Practices

1. Restrict access: Limit who can view forensic reports
2. Redact sensitive data: Remove PII before analysis/sharing
3. Secure storage: Encrypt forensic report archives
4. Data retention: Delete old reports according to policy
5. Compliance: Ensure GDPR/privacy law compliance

Sharing Forensic Reports

Be cautious when sharing:

• Never include original message content
• Redact sender/recipient addresses
• Remove subject lines with sensitive info
• Share only failure reason and metadata

Integrating Forensic Data with Security Tools

SIEM Integration

Send forensic data to security tools:

• Parse report emails automatically
• Extract IPs and domains
• Correlate with other security events
• Alert on suspicious patterns

SOAR Playbooks

Automate response:

• When spoofing attempt detected → block IP
• When new service detected → research documentation
• When authentication failures spike → alert security team

Threat Intelligence

Use forensic data for broader insights:

• Identify attack patterns
• Track attacker infrastructure
• Share with industry groups
• Contribute to threat databases

Best Practices for Forensic Report Handling

1. Set Appropriate Report Preferences

v=DMARC1; p=reject; rua=mailto:[email protected]; ruf=mailto:[email protected]; fo=1; rf=afrf; pct=100

• fo=1: Get forensic reports for all failures (better visibility)
• pct=100: Get reports for all messages initially
• rf=afrf: Use standard report format

2. Process Reports Regularly

• Review forensic reports daily or at minimum weekly
• Identify patterns and trends
• Track resolution of known issues
• Monitor DKIM/SPF pass rates

3. Maintain Forensic Infrastructure

• Keep forensic email addresses monitored
• Archive reports for historical analysis
• Implement automated parsing
• Set up alerts for anomalies

4. Correlate Multiple Data Sources

• Combine with aggregate reports
• Cross-reference with logs
• Verify with mail service documentation
• Check threat intelligence

5. Take Iterative Action

• Fix issues as identified
• Adjust DMARC policies gradually
• Test before enforcement
• Monitor results

Troubleshooting Common Issues

Not Receiving Forensic Reports

Possible causes:

• Reporting email address is wrong
• Email address isn't validated
• Forensic reports are disabled (fo=0)
• Reports being filtered as spam

Solutions:

# Verify DMARC record
dig _dmarc.yourdomain.com TXT

# Check reporting address is valid
dig yourdomain.com MX

# Ensure ruf parameter is correct
# Check spam filters for reports

Too Many Forensic Reports

Issue: Overwhelmed with false-positive forensic data

Solutions:

• Set fo=0 (only true failures)
• Adjust percentage sampling (pct=50)
• Filter reports by domain
• Implement automated filtering

Forensic Reports Won't Parse

Issue: Report format issues or corrupted data

Solutions:

• Verify reports are proper MIME format
• Check for encoding issues
• Ensure proper email parsing library
• Contact reporting organization

Conclusion

DMARC forensic reports provide valuable intelligence about mail authentication and potential abuse. By understanding how to interpret forensic data, categorize issues, and take appropriate action, organizations can:

• Identify legitimate mail infrastructure problems
• Detect and respond to spoofing attempts
• Improve email security posture
• Build comprehensive email authentication strategy

Effective forensic report handling requires regular monitoring, proper categorization, and systematic response to issues identified. Combined with aggregate reports and threat intelligence, forensic data becomes a powerful tool for understanding your email ecosystem and protecting against abuse.

Whether you're deploying DMARC for the first time or optimizing an existing implementation, paying attention to forensic report insights significantly improves your ability to secure email and prevent domain spoofing attacks.