Set Up DMARC RUA/RUF Reports and Analyze with OpenDMARC

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Every day, millions of domains are targeted by email spoofing, phishing, and other malicious activities. Implementing DMARC (Domain-based Message Authentication, Reporting & Conformance) is one of the most effective measures an organization can take to protect its domain from such abuse. A crucial aspect of a DMARC implementation includes setting up aggregate (RUA) and forensic (RUF) reports. These reports provide visibility into how email is behaving across the organization’s domains. To interpret and analyze these detailed reports effectively, tools like OpenDMARC can be incredibly helpful.

What is DMARC?

DMARC is an email validation system that builds on the SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) standards. When implemented, it helps domain owners:

  • Prevent unauthorized use of their email domain (email spoofing).
  • Gain insights into how their emails are being used and possibly abused.
  • Instruct receiving mail servers how to handle messages that fail authentication checks.

Understanding RUA and RUF Reports

DMARC supports two types of reports:

  • RUA (Aggregate Reports): These are XML-formatted summaries sent typically once a day by receiving servers. They contain data on the outcome of DMARC checks for all messages claimed to be from a domain.
  • RUF (Forensic Reports): These are more detailed and real-time reports of individual messages that failed DMARC checks. They may include message headers and sometimes even full message content, depending on configuration and receiving server capabilities.

1. Setting Up DMARC DNS Records for RUA and RUF

To begin receiving RUA and RUF reports, domain owners need to create or update a _dmarc DNS TXT record with the correct reporting addresses. Below is an example configuration:

_dmarc.yourdomain.com. IN TXT "v=DMARC1; p=none; rua=mailto:dmarc-rua@yourdomain.com; ruf=mailto:dmarc-ruf@yourdomain.com; fo=1;"

Here’s a breakdown of the elements:

  • v=DMARC1: Indicates the version.
  • p=none: The DMARC policy (none, quarantine, or reject).
  • rua: Destination for aggregate reports.
  • ruf: Destination for forensic reports.
  • fo=1: Instructs to send RUF reports for any failed authentication checks.

2. Setting Up Mailboxes to Receive Reports

Designate specific mailboxes capable of handling large volumes of XML files, especially if you operate a high-volume domain. It’s recommended to set up at least two email addresses, one for RUA and one for RUF. Ensure these addresses are ready to handle file attachments and are secured appropriately.

You may also use third-party DMARC report aggregators or email security services that will parse these reports on your behalf. However, if you prefer to retain control of your data analysis, using OpenDMARC is a powerful solution.

3. Installing and Configuring OpenDMARC

OpenDMARC is a free and open-source package developed by Trusted Domain Project, enabling DMARC filtering and report analysis. It comprises two main components: the OpenDMARC filter and the OpenDMARC report analyzer.

To install OpenDMARC on a Linux server (e.g., Debian-based), run:

sudo apt-get install opendmarc

Post-installation, you’ll need to configure it in /etc/opendmarc.conf. Example configurations:

Socket inet:8893@localhost
UserID opendmarc:opendmarc
Syslog yes
UMask 007
PidFile /var/run/opendmarc/opendmarc.pid
SoftwareHeader true
IgnoreAuthenticatedClients true
SPFIgnoreResults false

Restart the service after making changes:

sudo systemctl restart opendmarc

4. Collecting and Parsing DMARC Reports with OpenDMARC

Once DMARC is running and reports start arriving at your mailbox, you need to extract and parse the XML files. OpenDMARC includes a utility called opendmarc-import, which reads XML into its reporting database.

To parse the reports:

  1. Set up an IMAP or POP3 connection to the mailbox collecting reports.
  2. Use a tool to download the XML attachments (e.g., getmail, fetchmail, or custom scripts).
  3. Run the import command: 
    sudo /usr/sbin/opendmarc-import --dbhost=localhost --dbuser=opendmarc --dbpasswd=yourpass --dbname=opendmarc /path/to/XML/files/

5. Analyzing The Data

Once the data is in the database, OpenDMARC provides a web-based interface and CLI tools to generate summary reports. This helps you evaluate:

  • Which IPs are sending mail on behalf of your domain.
  • How often emails are failing SPF, DKIM, or DMARC checks.
  • Whether any unauthorized mail servers are using your domain.

This analysis is critical in gradually moving from a DMARC policy of none to quarantine or reject, enhancing your domain’s email security posture.

6. Tips for Effective DMARC Monitoring

  • Start small: Begin with policy none and monitor reports for a few weeks.
  • Use subdomains: Deploy DMARC first on subdomains to minimize disruption.
  • Whitelist sending sources: Identify and configure SPF/DKIM for legitimate sending services.
  • Review reports regularly: Set up automated scripts to ingest and analyze the reports daily.

Conclusion

Implementing DMARC reporting and analyzing data with OpenDMARC empowers organizations to identify vulnerabilities, authenticate legitimate email sources, and deter phishing attacks. While initial setup requires some technical investment, the long-term security and reputational benefits make it worthwhile. By combining DMARC policies with continuous reporting and insightful analytics, domain owners can build a robust and trustworthy emailing environment.

FAQs

What is DMARC used for?
DMARC (Domain-based Message Authentication, Reporting & Conformance) helps prevent email spoofing and provides a way for domain owners to request reports about email authentication results.
What’s the difference between RUA and RUF reports?
RUA reports are daily aggregate summaries of email authentication results, while RUF reports are real-time forensic reports that provide detailed information about failed emails.
Why should I use OpenDMARC instead of a third-party tool?
Using OpenDMARC allows you to keep sensitive data in-house, offers granular control, and lets you integrate the tool directly with your email systems and existing infrastructure.
Is it risky to collect RUF reports with payloads?
Yes, because RUF reports may contain personally identifiable information or message content. Always handle such data securely and ensure compliance with privacy regulations.
How soon should I change my DMARC policy from ‘none’ to ‘reject’?
Move to stricter policies only after reviewing reports over several weeks, confirming legitimate sources are authenticated, and ensuring minimal false positives.