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  • 24 Jun 2024

Understanding DKIM and DMARC

Before diving into their roles in a mailing infrastructure, it’s essential to understand what DKIM and DMARC are and how they function.

What is DKIM?

DKIM is an email authentication method that allows the recipient to check if an email claimed to have come from a specific domain was indeed authorized by the owner of that domain. It uses a pair of cryptographic keys—one private and one public—to create a digital signature for each email.

  • Private Key: Used by the sending mail server to generate a unique DKIM signature, which is added to the email header.
  • Public Key: Published in the DNS records of the sender’s domain, allowing the recipient’s mail server to verify the signature.

When an email is received, the recipient’s mail server retrieves the public key from the DNS records and uses it to validate the DKIM signature. If the signature matches, the email is considered authentic and unaltered.

What is DMARC?

DMARC builds on the foundations of SPF (Sender Policy Framework) and DKIM to provide an additional layer of protection. It aligns the results from SPF and DKIM checks and allows domain owners to specify how unauthenticated emails should be handled.

  • Policy Definition: Domain owners define a DMARC policy in their DNS records, specifying how emails that fail SPF or DKIM checks should be treated (none, quarantine, or reject).
  • Reporting: DMARC provides aggregate and forensic reports, offering insights into email authentication results and potential abuse of the domain.

DMARC helps domain owners protect their domain from unauthorized use, ensuring that legitimate emails are properly authenticated and fraudulent ones are blocked.

The Role of DKIM in a Mailing Infrastructure

Enhancing Email Security

DKIM significantly enhances email security by ensuring that emails have not been altered in transit. When an email is sent, DKIM adds a unique signature based on the contents of the email and the sender’s private key. The recipient’s server can then verify this signature using the public key published in the sender’s DNS records. If the signature is valid, the email is authenticated as coming from the purported domain and confirmed to be untampered.

Protecting Brand Reputation

By authenticating emails, DKIM helps protect the sender’s brand reputation. It prevents cybercriminals from spoofing the sender’s domain and sending fraudulent emails that could harm the brand’s reputation. Customers and partners are more likely to trust emails that are properly authenticated, knowing they are legitimate communications from the sender.

Improving Email Deliverability

Emails that are authenticated with DKIM are less likely to be marked as spam or rejected by the recipient’s mail servers. Many email service providers (ESPs) and Internet Service Providers (ISPs) use DKIM as a factor in their spam filtering algorithms. Authenticated emails have a higher chance of reaching the recipient’s inbox, improving overall email deliverability rates.

The Role of DMARC in a Mailing Infrastructure

Coordinating Email Authentication

DMARC coordinates the use of SPF and DKIM to provide a comprehensive email authentication strategy. By aligning the results of SPF and DKIM checks, DMARC ensures that emails are properly authenticated using both methods. This alignment enhances the overall security and integrity of email communications.

Defining Email Handling Policies

DMARC allows domain owners to define policies on how to handle emails that fail authentication checks. The three primary policies are:

  • None: No specific action is taken, but reports are sent to the domain owner.
  • Quarantine: Emails that fail authentication are marked as spam or placed in the recipient’s junk folder.
  • Reject: Emails that fail authentication are rejected outright and not delivered to the recipient.

By specifying these policies, domain owners can control the handling of unauthenticated emails and protect their domain from abuse.

Providing Visibility and Reporting

One of the most significant benefits of DMARC is its reporting capability. DMARC generates two types of reports:

  • Aggregate Reports: Provide a summary of email authentication results, including the number of emails that passed or failed SPF and DKIM checks.
  • Forensic Reports: Offer detailed information about individual emails that failed authentication, helping domain owners investigate potential issues or abuse.

These reports give domain owners valuable insights into their email traffic, allowing them to identify and address potential threats and improve their email authentication strategy.

Building Trust and Enhancing Security

By implementing DMARC, domain owners can build trust with their customers and partners. DMARC ensures that only legitimate emails from the domain are delivered, reducing the risk of phishing and spoofing attacks. Customers and partners are more likely to trust communications from a domain that has implemented DMARC, knowing that the domain is protected against unauthorized use.

Implementing DKIM and DMARC in Your Mailing Infrastructure

Steps to Implement DKIM

  1. Generate DKIM Keys: Use your email service provider’s tools to generate a pair of DKIM keys (private and public).
  2. Publish the Public Key: Add the public key as a TXT record in your domain’s DNS settings.
  3. Enable DKIM Signing: Configure your mail server to sign outgoing emails with the private key.
  4. Verify DKIM Configuration: Use online tools to verify that DKIM is correctly configured and functioning.

Steps to Implement DMARC

  1. Create a DMARC Policy: Define a DMARC policy specifying how to handle unauthenticated emails.
  2. Add a DMARC Record: Publish the DMARC policy as a TXT record in your domain’s DNS settings.
  3. Monitor DMARC Reports: Regularly review aggregate and forensic reports to understand email authentication results and identify potential issues.
  4. Adjust DMARC Policy: Based on the insights from the reports, adjust the DMARC policy as needed to enhance email security.


DKIM and DMARC are essential components of a robust email authentication strategy. By implementing these protocols, businesses can enhance email security, protect their brand reputation, and improve email deliverability. DKIM ensures that emails are authenticated and unaltered, while DMARC coordinates the use of SPF and DKIM, defines email handling policies, and provides valuable reporting insights. Together, DKIM and DMARC play crucial roles in securing a mailing infrastructure and building trust with customers and partners. Implement these protocols today to safeguard your email communications and protect your domain from email-based threats.

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