Can I set DMARC to reject if my domain doesn't send email?

Key findings

• Spoofing prevention: Setting a DMARC p=reject policy on a non-sending domain is highly effective at preventing unauthorized parties from spoofing your domain. This ensures that any email appearing to originate from your domain, but not genuinely sent by you, will be blocked by recipient servers.
• Reputation protection: Even if your domain doesn't send marketing or transactional emails, it can still be targeted by malicious actors. A p=reject policy helps protect your domain's reputation from being tarnished by phishing or scam campaigns.
• Compliance with checkers: Many security tools and checkers flag domains without DMARC records or with lenient policies. Implementing p=reject satisfies these requirements, improving your security posture in automated assessments.
• Simplicity: For a domain that genuinely sends no email, the DMARC record can be simple, often just specifying v=DMARC1; p=reject; though it's still advisable to include a reporting address to monitor any unexpected activity.

Key considerations

• Hidden sending sources: Before deploying p=reject, thoroughly investigate if your domain or any subdomains are inadvertently sending email. This includes website contact forms, server-generated alerts, CRM integrations, or legacy systems. Even minor, unexpected email flows could be blocked. Review our guide on how to configure DMARC for non-sending domains.
• Subdomain impact: A DMARC record at the organizational domain level applies to all subdomains unless explicitly overridden. Ensure no subdomains are legitimately sending email without their own DMARC records.
• Reporting (optional but recommended): Even for non-sending domains, including rua and ruf (reporting) tags can provide valuable insight into attempted spoofing. While it might seem unnecessary for a non-sending domain, these reports can alert you to malicious activity. Learn more about DMARC tags and their meanings. A guide by Mailgun elaborates on DMARC's instruction to ISPs to reject fraudulent emails.
• Gradual implementation: If there's any uncertainty about email sending, starting with p=none to gather reports before moving to p=reject is a safer, albeit more involved, approach.

Key opinions

• Default to reject for non-senders: The consensus among marketers is that if a domain is genuinely not sending email, setting p=reject is the ideal, secure configuration.
• Tool satisfaction: Many internal security or auditing tools will flag domains without DMARC or with weaker policies. Setting p=reject can resolve these flags and improve compliance scores.
• Security benefits: It's seen as a crucial step for preventing brand impersonation and protecting users from phishing attacks that might use the non-sending domain.
• Consider p=none first: If there's any doubt about whether the domain sends email, a safer initial approach is to start with p=none to monitor DMARC reports for a period.

Key considerations

• Thorough audit: Before switching to p=reject, conduct a comprehensive audit for any email-sending functions tied to the domain or its subdomains, such as contact forms, CRM integrations, or internal system notifications. This includes ensuring no legitimate emails will be blocked.
• Management communication: It's important to communicate with management, particularly if the decision is to set p=reject from day one, to ensure everyone understands that any potential, unexpected email from that domain will be blocked. Consider our guide on safely implementing DMARC p=reject.
• Subdomain configuration: Remember that a DMARC record at the main domain applies to subdomains. If any subdomain sends email, it will need its own DMARC record or its traffic will also be subject to the main domain's p=reject policy.

Key opinions

• Direct to reject: If it's absolutely certain no mail is sent from the domain or its subdomains, experts advocate for setting p=reject from day one to maximize security benefits.
• Simpler deployment: For non-sending domains, a p=reject policy avoids the complexities of a full DMARC deployment, which would typically involve monitoring reports and gradually increasing enforcement for active senders.
• Proactive security: This configuration is a strong proactive measure against email-based threats, safeguarding the domain's integrity.
• Start with p=none if unsure: In cases of uncertainty regarding email sending, beginning with p=none is a recommended initial step to gather data before moving to a stricter policy.

Key considerations

• Explicit confirmation of no sending: It's paramount to confirm that no email (including from any subdomains or superdomains) is sent using that domain in the From: address. This requires collaboration with sysadmins and hosting providers to identify all potential email sources. Our guide on configuring DMARC, SPF, and DKIM for non-sending domains details this.
• Stakeholder alignment: Ensure senior management is aware and provides written understanding that any legitimate mail inadvertently sent from the domain will be intentionally broken (rejected). This minimizes future issues. For deeper insights, consult use cases for DMARC policies.
• Reporting for vigilance: While not strictly necessary to enforce rejection, setting up DMARC reporting (rua) can still be beneficial. It allows monitoring for any unexpected spoofing attempts or accidental sending from the domain, even if no legitimate mail is expected. Consider reviewing how to interpret DMARC reports.

Key findings

• Policy enforcement: The DMARC p=reject policy explicitly instructs email receivers to refuse delivery of messages that fail DMARC authentication, effectively blocking them at the gateway.
• Authentication standards: DMARC leverages existing email authentication protocols, SPF and DKIM, to verify the legitimacy of emails. A p=reject policy means messages must pass at least one of these and have identifier alignment.
• Domain ownership assertion: By publishing a DMARC record, a domain owner asserts control over how mail purporting to be from their domain should be handled, providing a layer of trust for receivers.
• Subdomain inheritance: Without explicit DMARC records for subdomains, they inherit the policy of the organizational domain. This is critical for domains not sending mail, as it extends protection automatically.

Key considerations

• DNS record placement: The DMARC record is a TXT record placed in the DNS, allowing receiving mail servers to query it and determine how to handle messages. A p=reject policy is specified within this record.
• Aggregate and forensic reports: Even for non-sending domains, including rua (aggregate) and ruf (forensic) reporting tags allows the domain owner to receive data on mail flows claiming to be from their domain. This helps identify attempted spoofing. Further details are available in a guide to DMARC tags and their meanings.
• Policy deployment: While p=reject can be implemented immediately for non-sending domains, documentation often advises a phased rollout (p=none, then p=quarantine, then p=reject) for active sending domains to prevent legitimate mail from being blocked. Review the understanding of DMARC policies.