by Chuck Mackey and Will Hudec
What is DMARC?
DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a powerful email authentication protocol designed to protect your email domain from being impersonated. It works by comparing the sender address to authentication information in the email to verify the message is really from your domain.
How does it work?
When you enable DMARC, receiving email services will check incoming emails that claim to be from your domain against your DMARC settings. If the email fails the DMARC check, it can be rejected or treated with suspicion.
Why is it important?
- Prevents attackers from sending emails that appear to come from your domain
- Allows recipients to identify and reject spoofed/phished emails
- Gives visibility into misuse of your domain for sending emails
- Enforces email authentication policies across your domain
The DMARC protocol increases the trustworthiness of your domain and enhances email deliverability. While it is an essential tool in your email security toolkit, it should be part of a broader email security strategy that includes other measures such as user training, strong passwords, and regular security updates.
Fortress Security Risk Management provides the following best practices for establishing and optimizing DMARC:
1. Understand DMARC Basics:
Familiarize yourself with the DMARC protocol and how it works. It builds upon SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) to add an additional layer of protection.
2. Gradual Deployment:
Start with a “p=none” policy, which monitors and reports but doesn’t enforce. This allows you to understand the email landscape for your domain without affecting email delivery.
3. Publish DMARC Records:
Publish a DMARC DNS record for your domain. This record specifies your DMARC policy, how to manage emails that don’t pass authentication, and where to send aggregate and forensic reports.
4. Alignment of SPF and DKIM:
Ensure that SPF and DKIM records are properly configured and aligned with your DMARC policy. The “alignment” is crucial for DMARC to work effectively. Make sure the “From” domain in the email header aligns with your SPF and DKIM.
5. Use DKIM Signatures:
Always use DKIM signatures for your outgoing emails. This ensures that email recipients can verify the authenticity of your messages.
6. Subdomain Policy:
Consider setting separate DMARC policies for your subdomains. You can start with a less strict policy for subdomains and tighten it as needed.
7. Use Reporting:
Configure DMARC to send reports to your specified email address. These reports provide valuable insights into the sources and results of email authentication checks, helping you identify any issues.
8. Review DMARC Reports:
Regularly analyze DMARC reports to understand who is sending emails on behalf of your domain. Look for anomalies and unauthorized senders.
9. Gradual Policy Enforcement:
Once you’ve gathered enough data and are confident in your email infrastructure, switch to a “p=quarantine” or “p=reject” policy to stop unauthorized emails. Be cautious about moving too quickly, as it can lead to legitimate emails being rejected.
10. Authenticity Checks:
Ensure that your email authentication methods, such as SPF and DKIM, are correctly implemented. Review the DMARC reports for any authentication failures and resolve them.
11. Monitor Email Deliverability:
Continuously monitor email deliverability to ensure that legitimate emails aren’t being blocked or sent to spam. Keep an eye on bounce rates, engagement metrics, and feedback loops.
12. Implement DMARC Alerts:
Configure email alerts to notify you of any DMARC policy failures. This way, you can take immediate action if your domain is being abused.
13. Maintain a DMARC Record:
Regularly review and update your DMARC record as your email infrastructure evolves.
14. Education and Training:
Educate your team and users about the importance of DMARC and how it helps protect against phishing. Encourage them to be vigilant and report any suspicious emails.
15. Seek Professional Assistance:
If you’re unsure about DMARC implementation, consider seeking the assistance of email security expertise from Fortress SRM for using email security tools and services.
Properly implementing DMARC provides strong protection against email spoofing and phishing attacks, giving recipients high confidence in the authenticity of emails from your domain.
About Fortress SRM:
Fortress Security Risk Management protects companies from the financial, operational, and emotional trauma of cybercrime by enhancing the performance of their people, processes, and technology.
Offering a robust, co-managed solution to enhance an internal IT team’s capability and capacity, Fortress SRM features a full suite of managed security services (24/7/365 U.S. based monitoring, cyber hygiene (managed patching), endpoint detection and response (EDR), and air-gapped and immutable cloud backups) plus specialized services like Cybersecurity-as-a-Service, Incident Response including disaster recovery & remediation, M&A cyber due diligence, GRC advisory, identity & access management, threat intelligence, vulnerability assessments, and technical testing. With headquarters in Cleveland, Fortress SRM supports companies with both domestic and international operations.
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