How to identify and handle spoofed emails violating DMARC policies?

Key findings

• DMARC reports: DMARC aggregate reports are the primary source for detecting unauthorized sending from your domain, providing data on who is sending, even if they fail authentication.
• IP identification: Reports provide the IP addresses of the senders, which can be used for reverse lookups (e.g., ARIN search) to identify the network owner.
• Domain targeting: Domains can be randomly chosen targets for spoofing, leading to significant volumes of unauthorized emails originating from various global networks.
• Policy enforcement: A DMARC policy set to 'reject' instructs receiving servers to block unauthorized emails, preventing them from reaching inboxes.
• Alerting teams: An uptick in DMARC violations, especially under a 'reject' policy, may necessitate alerting security and support teams about potential intrusion attempts or increased help requests due to bounced emails.

Key considerations

• Proactive monitoring: Regularly analyzing DMARC reports is essential to detect and respond to spoofing attempts effectively. This aligns with advice on analyzing aggregate reports.
• Policy strength: While `p=none` offers visibility, gradually moving to `p=quarantine` or `p=reject` provides stronger protection against spoofing.
• Understanding failures: Even with a 'reject' policy, understanding why DMARC authentication might fail for legitimate mail or what specific threats are present is crucial.
• Beyond DMARC: Consider whether spoofing attempts might be linked to other security threats, such as phishing campaigns or penetration testing.

Key opinions

• Data importance: Access to DMARC reports is essential for understanding who is attempting to send email from a domain, even if unauthorized.
• IP lookup: Using tools like ARIN to look up IP addresses from DMARC reports helps identify the owners and abuse contacts of the sending infrastructure.
• Common occurrence: It is not uncommon for a domain to be randomly selected as a target for spoofing, leading to high volumes of unauthorized mail.
• Policy effectiveness: A DMARC policy set to 'reject' is expected to prevent spoofed emails from reaching inboxes, though understanding its full implications is key.
• Security implications: Increased DMARC violations, even with a 'reject' policy, could signal a need for support and security teams to prepare for more help requests or potential intrusion attempts.

Key considerations

• DMARC report analysis: Marketers should actively interpret DMARC reports to pinpoint unauthorized sending sources.
• Policy understanding: It is important for marketers to grasp the differences and implications of 'none', 'quarantine', and 'reject' DMARC policies, as explained in resources like understanding DMARC policies.
• Proactive steps: Even with DMARC in place, marketers might question if passive waiting for spoofing campaigns to cease is the only recourse, emphasizing the need for ongoing vigilance and actions when a domain is spoofed.
• Policy review: Regular review of SPF, DKIM, and DMARC policies is necessary to ensure proper configuration and prevent easy spoofing, as well as considering unusual scenarios like penetration testing.

Key opinions

• Primary defense: DMARC is considered the most effective defense against direct domain spoofing, providing a mechanism to block unauthorized email.
• Reporting insights: DMARC aggregate reports are invaluable for identifying unexpected sending sources and understanding the scope of spoofing attempts targeting a domain.
• Policy goal: The ultimate goal for domain protection is to achieve a DMARC 'reject' policy, ensuring that unauthenticated mail is definitively blocked.
• Alignment focus: Ensuring SPF and DKIM alignment with the `From:` domain is critical for DMARC to pass, making it a key focus for authentication success.
• Attribution challenges: While DMARC reports identify sending IPs, pinpointing the specific malicious actors behind spoofing can be a complex task.

Key considerations

• Phased implementation: Experts recommend a gradual transition from `p=none` to `p=quarantine` and then `p=reject` to safely implement DMARC policies.
• Comprehensive analysis: Beyond just seeing failures, understanding the forensic details (`fo` tag) in DMARC reports helps track down unauthorized senders.
• Legitimate mail impact: Misconfigured SPF or DKIM records, or issues with email forwarding, can inadvertently cause legitimate email to fail DMARC checks. For further reading, consult resources like Mailgun's guide to DMARC implementation.
• Continuous monitoring: Even with a 'reject' policy, continuous monitoring of DMARC reports is vital, as some receivers might still process failed messages differently.

Key findings

• Authentication foundation: DMARC builds upon existing email authentication protocols, SPF and DKIM, to verify email authenticity.
• Policy directives: DMARC policies allow domain owners to specify how receiving mail servers should treat messages that fail authentication, ranging from monitoring to rejecting.
• Reporting mechanism: The protocol includes a reporting mechanism (RUA and RUF tags) that provides domain owners with feedback on DMARC validation results.
• Domain alignment: DMARC requires alignment between the `From:` header domain and the domains verified by SPF or DKIM to pass authentication.
• Spoofing protection: The primary goal of DMARC is to protect against email impersonation and direct domain spoofing by providing strong policy enforcement capabilities.

Key considerations

• Policy progression: Documentation generally advises starting with a `p=none` policy to gather data before transitioning to stricter `p=quarantine` or `p=reject` policies. You can explore simple DMARC examples.
• DNS configuration: Proper DNS record configuration for SPF, DKIM, and DMARC is fundamental for their correct operation and effectiveness against spoofing.
• Understanding tags: Familiarity with various DMARC tags and their meanings, such as `rua` for aggregate reports and `ruf` for forensic reports, is important for comprehensive monitoring.
• Beyond authentication: While DMARC helps, understanding general email spoofing techniques, as detailed in SentinelOne's guide, provides a broader security perspective.