DMARC (Domain-based Message Authentication, Reporting, and Conformance) is an email authentication technology that helps organizations protect their domains from misuse, such as phishing and spoofing. DMARC combines and utilizes the standards of SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail), adding reporting capabilities and policies for handling emails that fail authentication.

Basic Principles of DMARC

1. SPF and DKIM as the Foundation

DMARC requires that the mechanisms of SPF and DKIM be correctly set up and used. SPF verifies the sender's IP address, while DKIM verifies the signature in the email header. These standards provide the foundational layer of authentication on which DMARC builds.

2. DMARC Record Tags

A DMARC record is published in the DNS records of a domain and contains several key tags:

• v=DMARC1: The version of the DMARC record.
• p=: Policies for handling emails that fail verification (none, quarantine, reject).
• rua=: Address for sending aggregate reports.
• ruf=: Address for sending forensic reports.
• pct=: The percentage of emails to which the policies are to be applied.
• adkim=: Alignment mode for evaluating DKIM (s - strict, r - relaxed).
• aspf=: Alignment mode for evaluating SPF (s - strict, r - relaxed).

Setting DMARC Policies

1. No Action (p=none)

This is the initial phase of DMARC implementation, where emails that fail verification are only reported, but otherwise not processed or restricted. This setting is recommended at the start of DMARC deployment to gather data and analyze.

2. Quarantine (p=quarantine)

In this phase, emails that fail verification are redirected to quarantine (such as a spam folder). This setting is a middle ground that allows organizations to gradually increase the rigor of their email policy.

3. Reject (p=reject)

The strictest DMARC setting. Emails that fail verification are completely rejected and not delivered to the recipient. This setting is recommended after thorough analysis and testing to avoid the unintended rejection of legitimate emails.

Benefits and Risks of DMARC

Benefits

• Increased credibility of emails from the domain.
• Protection of the brand and users from phishing and spoofing attacks.
• Improved visibility and control over email communication through reports.

Risks

• Strict settings without adequate testing can lead to the rejection of legitimate emails.
• The need for correct SPF and DKIM configuration for DMARC to function effectively.

DMARC is a significant tool in the fight against the misuse of email domains. With proper setting and gradual implementation, it can greatly improve the security and credibility of email communication. The key is careful preparation, testing, and ongoing analysis of reports to optimize settings.