Whats DMARC?

DMARC is an email authentication protocol that helps protect against domain spoofing and email impersonation. It allows domain owners to specify how email receivers should handle emails claiming to originate from their domain. DMARC works by providing a policy that instructs email receivers to reject, quarantine, or deliver emails based on their alignment with established authentication mechanisms like SPF and DKIM (DomainKeys Identified Mail).

By implementing DMARC, organizations can monitor and enforce email authentication practices, gain visibility into email flows, and receive reports on emails that fail authentication checks. This protocol strengthens email security and helps prevent phishing attacks that exploit domain impersonation.

DMARC is an essential email security standard that enables domain owners to monitor and control the legitimacy of email messages sent using their domain. It provides instructions to email receivers, such as Gmail, regarding the approval, quarantine, or rejection of emails that do not originate from an authenticated source.

What Is DMARC?

The primary purpose of DMARC is to prevent domain impersonation, commonly known as spoofing, and to protect recipients from falling victim to phishing attempts. It ensures that fraudulent emails, like PayPal phishing scams, are blocked before reaching the recipients’ inboxes, safeguarding sensitive information and preserving domain reputations.

DMARC functions by leveraging two email authentication technologies: DKIM (DomainKeys Identified Mail) and SPF (Sender Policy Framework). DKIM verifies the integrity of messages during transit, while SPF validates that the email originated from an authorized server. DMARC instructs inbox providers to consider a message legitimate if either DKIM or SPF authentication passes. If both fail or are absent, the provider should treat the message with suspicion and take action according to the domain’s DMARC policy.

DMARC policies determine the actions to be taken by email receivers when a message fails the DMARC check. There are three DMARC policies available:

1. Approve or monitor policy (p=none): The receiver delivers the email normally, even if it fails DMARC.
2. Quarantine policy (p=quarantine): The receiver treats the message as suspicious and directs it to the recipient’s spam folder.
3. Reject policy (p=reject): The receiver discards the message and does not deliver it to the user.

To implement DMARC as part of the overall information security management system of an organization, The organizations need to have SPF and DKIM already in place. They then add a DMARC DNS record to their domain configuration. The record specifies the DMARC version, domain policy, subdomain policy, percentage of messages the policy applies to, and the address for aggregate reports.

Implementing DMARC requires careful attention and consideration to avoid unintended consequences. Incorrect configuration may result in the rejection of legitimate emails. It is essential to thoroughly understand all email sources within an organization, such as mailboxes, email marketing platforms, CRM systems, and transactional email services, to ensure proper configuration and prevent legitimate messages from being erroneously rejected.

How DMARC works?

Example 1: Successful DMARC Authentication
Suppose a legitimate organization, “ABC Corp,” has implemented DMARC for its domain, “abccorp.com.” When an email is sent from an authorized server, such as “mailserver.abccorp.com,” the email includes a DMARC record in its header. The recipient’s mail server checks the DMARC record published in DNS for the “abccorp.com” domain. If the email passes the SPF and DKIM authentication checks defined in the DMARC policy, it is considered authenticated and delivered to the recipient’s inbox which improve our overall isms (whats ISMS?) organizational security strategy.

Example 2: Failed DMARC Authentication
In another scenario, an attacker attempts to impersonate ABC Corp by sending a phishing email from a malicious server, “fake.abccorp-phish.com.” The recipient’s mail server receives the email and checks the DMARC record for “abccorp.com.” Since the malicious server “fake.abccorp-phish.com” is not listed as an authorized server in the SPF record or fails the DKIM signature check, the email fails DMARC authentication. According to the DMARC policy set by ABC Corp, the email can be quarantined or rejected, protecting the recipient from falling victim to the phishing attempt.

Example 3: DMARC Aggregate Reports
DMARC also provides valuable feedback through aggregate reports. These reports provide domain owners with insights into email authentication results and potential abuse attempts. For example, ABC Corp receives DMARC aggregate reports that highlight failed authentication attempts from unauthorized servers claiming to send emails on behalf of their domain. By analyzing these reports, ABC Corp can identify patterns, take corrective actions, and strengthen their email security posture. could be part of what company internal job roles like “cyber security analyst” would do to actively protect the organization as part of a timely manner strategic approach of ISMS, meaning that once every X amount of time we want our security analyst to go over accessible reports and logs and find patterns and attacks on our organization.

By implementing DMARC correctly, organizations can significantly enhance their email deliverability, protect their domain reputation, and mitigate the risk of falling victim to phishing attacks.