DMARC-records begrijpen en toevoegen aan DNS

What Is DMARC?

Email remains one of the most important communication channels for bedrijven, but it is also one of the most commonly abused. Cybercriminals frequently attempt to impersonate legitimate domains through phishing, spoofing, and business email compromise attacks.

Domain-based Message Authentication, Rapportage, and Conformance (DMARC) is an email authentication standard designed to protect domains from unauthorized email use. It works alongside two other email security technologies:

• Kader voor afzenderbeleid (SPF)
• DomainKeys geïdentificeerde e-mail (DKIM)

Samen, these technologies help receiving mail servers determine whether incoming messages are legitimate or potentially fraudulent.

DMARC provides instructions that tell receiving servers how to handle messages that fail authentication checks, helping domain owners reduce the risk of spoofed emails reaching users.

Why DMARC Matters

Without proper email authentication, attackers can forge your domain name and send messages that appear to originate from your organization.

Potential risks include:

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• Phishing attacks
• CEO fraud
• Credential theft
• Malware delivery
• Brand reputation damage
• Customer trust issues

DMARC helps reduce these threats by enforcing authentication policies and providing visibility into how your domain is being used across the internet.

How DMARC Works

DMARC relies on SPF and DKIM validation.

When an email is received, the receiving mail server performs several checks:

1. Verify SPF authentication.
2. Verify DKIM authentication.
3. Check domain alignment requirements.
4. Apply the DMARC policy.
5. Generate reports if configured.

Depending on the configured policy, messages that fail authentication can be:

• Allowed
• Quarantined
• Rejected

This process helps prevent unauthorized senders from abusing your domain.

What Is a TXT Record?

DNS TXT records are special DNS entries that store text-based information.

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They are commonly used for:

• Domain verification
• SPF records
• DKIM records
• DMARC policies
• Third-party service validation

DMARC is implemented through a TXT record published in DNS.

Mail servers query this record to determine how authentication failures should be handled.

What Is a DMARC TXT Record?

A DMARC record is a specially formatted TXT record that contains policy instructions for email authentication.

The record is published under a dedicated DNS hostname:

_dmarc.yourdomain.com

When a receiving mail server processes a message claiming to originate from your domain, it retrieves this record and follows the specified policy.

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Example DMARC Record

A simple DMARC record may look like:

v=DMARC1; p=none; rua=mailto:[email protected]

This record contains several tags that define how DMARC operates.

Understanding DMARC Tags

v Tag

The version tag identifies the DMARC protocol version.

Voorbeeld:

v=DMARC1

Momenteel, DMARC1 is the standard version used across the industry.

p Tag

The policy tag defines how failed messages should be handled.

Voorbeeld:

p=none

This is the most important part of the record because it controls enforcement behavior.

rua Tag

The Reporting URI for Aggregate Reports.

Voorbeeld:

rua=mailto:[email protected]

Aggregate reports provide visibility into authentication results and email activity associated with your domain.

These reports are typically delivered daily by participating mail providers.

DMARC Policy Types

The policy tag determines the action taken when a message fails authentication.

None Policy

p=none

Behavior:

• No enforcement action
• Messages continue to be delivered normally
• Reports are generated

This policy is commonly used during initial deployment because it allows administrators to monitor authentication results before enforcing stricter controls.

Quarantine Policy

p=quarantine

Behavior:

• Failed messages are treated as suspicious
• Messages may be delivered to spam or junk folders

This policy provides moderate protection while still allowing administrators to review potentially legitimate messages.

Reject Policy

p=reject

Behavior:

• Failed messages are rejected entirely
• Messages never reach the recipient mailbox

This is the strongest DMARC policy and offers the highest level of protection against spoofing attacks.

Understanding DMARC Reports

DMARC reporting provides valuable insight into how email is being sent from your domain.

Reports help identify:

• Unauthorized senders
• Misconfigured email services
• Spoofing attempts
• Authenticatiefouten
• SPF alignment issues
• DKIM alignment issues

Organizations often use these reports to fine-tune their email authentication strategy before moving to stricter policies.

Common DMARC Reporting Types

Aggregate Reports (RUA)

Aggregate reports provide summarized authentication data from participating mail providers.

These reports typically include:

• Sending IP addresses
• Authentication results
• Message volumes
• SPF status
• DKIM status

Forensic Reports (RUF)

Forensic reports provide detailed information about individual authentication failures.

Because of privacy considerations, support for forensic reporting varies between providers.

Creating a DMARC Record

Before publishing a DMARC policy, ensure that SPF and DKIM are already configured correctly.

Without SPF and DKIM alignment, DMARC enforcement may inadvertently block legitimate email.

Check Existing DNS Records

Before creating a new record, verify whether a DMARC record already exists.

Several DNS analysis tools can help verify current configuration.

Veel voorkomende opties zijn onder meer:

• MxToolbox DMARC Lookup
• DMARC analyzers
• DNS inspection tools

Enter your domain name and check whether a DMARC TXT record is already present.

Access DNS Management

To add or modify a DMARC record, access the DNS management interface used by your domain.

This may be located within:

• Domain registrar dashboards
• Hosting control panels
• DNS hosting providers
• CDN platforms

Once inside the DNS management area, you can create or edit records.

Methode 1: Manually Create a DMARC Record

Stap 1

Create a new DNS record.

Stap 2

Selecteer:

TXT

as the record type.

Stap 3

Set the hostname:

_dmarc

Stap 4

Add the DMARC value.

Voorbeeld:

v=DMARC1; p=none; rua=mailto:[email protected]

Stap 5

Save the record.

DNS propagation may require some time before the record becomes visible globally.

Methode 2: Use a DMARC Generator

Many DNS providers and email security platforms include DMARC generation tools.

These tools simplify configuration by allowing administrators to select options through a graphical interface.

Typical steps include:

1. Open the email security section.
2. Select DMARC configuration.
3. Enter a reporting email address.
4. Choose a policy.
5. Define enforcement settings.
6. Generate the record.
7. Publish the generated TXT record.

This method reduces the chance of syntax errors.

Recommended Deployment Strategy

For new deployments, avoid immediately enforcing a reject policy.

A common rollout strategy is:

Phase 1

Monitor only:

p=none

Collect reports and verify all legitimate mail sources.

Phase 2

Increase protection:

p=quarantine

Monitor results and resolve any remaining authentication issues.

Phase 3

Full enforcement:

p=reject

Once all legitimate senders pass SPF and DKIM validation, move to full rejection.

This gradual approach minimizes the risk of accidentally blocking valid messages.

Best Practices for DMARC

Configure SPF and DKIM First

DMARC depends on proper SPF and DKIM alignment.

Verify both technologies before enabling enforcement.

Monitor Reports Regularly

Review aggregate reports to identify:

• Unauthorized senders
• Misconfigurations
• New email services

Use a Dedicated Reporting Address

Create a mailbox specifically for DMARC reports.

Voorbeeld:

[email protected]

This helps separate reporting traffic from normal business communications.

Enforce Gradually

Move from:

none → quarantine → reject

rather than enabling rejection immediately.

Audit Third-Party Senders

Verify that all legitimate services sending email on behalf of your domain are properly authorized.

Voorbeelden zijn onder meer:

• Marketing platforms
• Help desk systems
• CRM software
• Transactional email services

Strengthening Email Security with DMARC

DMARC is one of the most effective tools available for protecting domains against spoofing, phishing, and email impersonation attacks. By combining DMARC with SPF and DKIM, organizations gain greater control over how their domains are used and significantly improve email security.

A properly configured DMARC policy not only protects your organization but also improves email trustworthiness and increases the likelihood that legitimate messages reach their intended recipients.