DMARC FO Tag Explained: DMARC Failure Reporting Options

The DMARC fo tag determines failure reporting options within the DMARC protocol. While optional, it is an important component of DMARC authentication defining how failure reports (RUF) are generated.

Leveraging email authentication is an easy and helpful way to boost the security of email communications. DMARC (Domain-based Message Authentication, Reporting, and Conformance) is one of the many email authentication protocols of the email authentication process. It helps domain owners to specify their authentication procedure and protect their domains from unauthorized access and use.

Key Takeaways

Specifying Failure Reporting Options: The “fo” tag is an optional tag that helps define the types of authentication and alignment issues that should be reported.
Supporting Various Failure Types: It supports four types of DMARC failure reports: fo=0, fo=1, fo=d, and fo=s.
Possibility for Combination of Various Reporting Options: It is possible to combine several fo reporting options for a more personalized and targeted experience.
Best Practices: It is important to consistently monitor and examine the failure reports to ensure effective prevention of cyber threats.

What is the DMARC FO Tag?

The “fo” tag in DMARC stands for failure options. It is an optional tag that helps determine the types of authentication and alignment issues that should be reported. This enables domain owners to filter the reporting process, adjusting it to their unique business demands and requirements.

How DMARC Failure Reports Can Help You

DMARC reports can help you with their contents and actionable insights:

The Contents of DMARC Failure Reports

DMARC failure reports include important information about messages that failed authentication checks. More specifically, they include:

The sender’s IP address
The sending domain
The time of the message
The cause(s) behind the authentication failure
SPF and DKIM alignment results

Why It Matters

These reports will help you:

Find out which legitimate senders are failing authentication
Detect attempts of malicious activity (e.g. spoofing and phishing attacks)
Find mistakes and misconfigurations in your SPF or DKIM settings
Monitor how effective your DMARC implementation strategy is while also tracking any changes in effectiveness over time

DMARC FO Tag Options and Their Meanings

The “fo” DMARC tag supports four different options (i.e. four specific types of failure reports):

fo=0 (Default Option)

When using this option, a DMARC failure report is generated only if both SPF and DKIM (i.e. all the underlying authentication mechanisms) do not produce an aligned “pass” outcome. This means that fo=0 generates reports only for the most severe authentication failures.

fo=1 (Recommended Option)

This option instructs to generate a DMARC failure report if SPF or DKIM (i.e. any one of the underlying authentication mechanisms) does not provide an aligned “pass” outcome. This is the recommended option since it provides a more comprehensive reporting scheme.

fo=d (DKIM-specific Option)

When using this fo=d option, it triggers the generation of failure reports specifically for messages where the DKIM signature evaluation fails, irrespective of alignment status. This is particularly useful for domain owners who want to focus specifically on DKIM-related issues.

fo=s (SPF-specific Option)

This setting triggers the creation of failure reports exclusively for messages that do not pass SPF evaluation, regardless of their alignment status. This is the preferred option for domain owners who want to pay particular attention to SPF-related problems.

Combining Multiple Forensic Reporting Options

What is really great about the “fo” tag is the ability to combine multiple reporting options. This allows domain owners to create a customized reporting strategy that best suits their needs. To specify multiple types of reports, you can use a colon (:) to separate each option in the “fo” tag.

For example, if you wanted to receive reports for options 0, 1, and s, you would add a “fo” tag to your DMARC record like this:

fo=0:1:s

This configuration would generate reports for:

Complete authentication failures (0)
Any authentication mechanism failure (1)
SPF-specific failures (s)

When To Use Each Failure Reporting Settings: Examples & Best Practices

When implementing DMARC failure reporting, consider the following best practices:

Begin with the default “fo=0” to ensure your systems are not immediately overloaded with reports.
Gradually, move to “fo=1” for more comprehensive insights.
Use the “fo=d” if you need to focus on DKIM issues or “fo=s” in case you need more information on SPF issues.
Try combining options that align with your email authentication goals for a more customized approach.
Regularly monitor and analyze the failure reports to immediately address any relevant issues.

Setting Up a DMARC Record with the FO Tag

1. Create a DMARC Record

To set up DMARC with the forensic reporting option enabled, you need to create a TXT record. You can use our DMARC Record Generator tool to automate this process. This DMARC record specifies how the receiving server should handle messages failing authentication checks. You can define the “fo” tag within your DMARC record using the “fo=value” parameter.

Example of a DMARC record with the “fo” tag:

v=DMARC1; p=quarantine; rua=mailto:[email protected]; ruf=mailto:[email protected]; fo=1; pct=100;

2. Choose Your FO Setting

There are four options to choose from as discussed:

fo=0: To generate a failure report only if both SPF and DKIM fail. This option is recommended for minimal reporting and reducing unnecessary forensic reports.
fo=1: To generate a failure report if either SPF or DKIM fails. This option is useful for detailed reporting when troubleshooting authentication failures.
fo=d: To generate a failure report if DKIM fails. This option is ideal for organizations that rely heavily on DKIM authentication.
fo=s: To generate a failure report if SPF fails. This option is suitable when SPF is the primary authentication mechanism.

3. Add the DMARC Record to Your DNS

To set up DMARC with the “fo” tag enabled, you need to add your generated DMARC record to your DNS. To do so:

Log in to your domain registrar’s DNS management console.
Navigate to the DNS settings for your domain.
Add a new TXT record with the following details:

Host: _dmarc.example.com (replace example.com with your domain)

Type: TXT

Value: (Your DMARC record syntax)

Save changes and allow DNS propagation (can take up to 48 hours).
Check your DMARC record using a DMARC checker tool.

How to Monitor and Interpret DMARC Failure Reports

DMARC failure reports can provide deep insights into forensic incidents attempted on your domain. However, reading them can be a challenge! To monitor and interpret these reports easily:

Use a dedicated mailbox: It’s recommended to use a dedicated email address to receive your forensic reports. This will reduce inbox clutter and help you monitor your reports more efficiently.
Analyze reports: forensic reports are generated in XML (Extensible Markup Language). Those unfamiliar with it can use a DMARC report analyzer tool like the one PowerDMARC provides. This tool is an excellent alternative to manual interpretation, making the reports more organized and human-readable.
Identify malicious sources: You can use the information provided in your failure reports to swiftly identify malicious sending sources trying to spoof your domain.
Adjust your policies: Finally, it’s time to take action. If you recognize potential spoofing attempts on your domain, and your DMARC policy is not enforced – this spells trouble! Gradually shift to p=reject policy for DMARC to start preventing email threats.

Troubleshooting Common DMARC FO Issues

Misconfigured DMARC Records

Several reasons like DMARC record syntax errors, missing required tags, or incorrect formatting can cause failures. It’s advisable to use online DMARC record checkers to validate your record before publishing.

Incorrect FO Settings

If you are not receiving forensic reports or receiving incomplete reports, it can be due to incorrect tag settings. To fix this, ensure that:

The ruf tag is correctly set with a valid email address.
The email provider supports forensic reports.
The fo value is correctly configured based on your reporting needs.

SPF/DKIM Configuration Errors

Note that SPF or DKIM failures can affect your DMARC report results. To prevent unwarranted failures, make sure that you:

Verify SPF records have the correct sending IPs.
Ensure DKIM signatures are correctly aligned and published in DNS.
Test SPF and DKIM using online validation tools.

Responding to Failure Reports

Analyze Failures for Authorized Parties

Take immediate action if you notice that legitimate senders are also failing authentication. Work with the authorized senders to ensure their email configurations are correct. This will help improve the flow of email communications and effectively filter between legitimate and illegitimate sources.

Regularly update your DNS records

Carefully examine the findings of your DMARC failure reports. Then, adjust your SPF, DKIM, or DMARC records accordingly for a comprehensive security framework.

Take Action Against Unauthorized Senders

In case you notice any malicious activity or unauthorized use of your domain, block/report their IP addresses. This will help prevent data breaches and improve your overall security online.

Move Toward a Stricter Policy

As mentioned already, try gradually increasing your DMARC policy strictness. Transitioning from relaxed mode (i.e. p=none) to p=quarantine to p=reject will decrease the likelihood of successful cyberattacks on your domain.

Summing Up

Incorporating DMARC failure reporting with the “fo” tag is a strategic move toward strengthening your email security posture. By leveraging the right failure reporting options, domain owners can gain deeper visibility into authentication issues, detect malicious activity, and refine their email authentication strategy.

Regularly monitoring and analyzing these reports enables proactive adjustments, ensuring a well-protected domain. As cyber threats continue to increase by at least 30% year on year, fine-tuning your DMARC policy with effective failure reporting will help maintain trust in your communications.

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Ahona Rudra

Domain & Email Security Expert at PowerDMARC

Ahona is the Marketing Manager at PowerDMARC, with 5+ years of experience in writing about cybersecurity topics, specializing in domain and email security. Ahona holds a post-graduation degree in Journalism and Communications, solidifying her career in the security sector since 2019.