How to Implement DMARC

For Better Email Deliverability

How to Implement DMARC for Better Email Deliverability

Email deliverability is a critical concern for businesses and organizations relying on email for communication and marketing. One of the most effective ways to improve email security and deliverability is by implementing Domain-based Message Authentication, Reporting, and Conformance (DMARC). DMARC helps prevent email spoofing and phishing attacks, ensuring that legitimate emails reach inboxes while fraudulent emails are blocked or flagged.

This guide outlines the steps to implement DMARC effectively.

Understand DMARC and Its Components

DMARC builds on two existing email authentication protocols:

SPF (Sender Policy Framework)

SPF is an email authentication protocol to prevent email spoofing and phishing attacks. It helps email servers verify whether a sender is authorized to send emails on behalf of a domain.

How SPF Works
  1. Domain Owner Creates an SPF Record
    • The domain owner publishes an SPF record in the DNS (Domain Name System).
    • This record lists the authorized mail servers that can send emails on behalf of the domain.
  2. Recipient's Mail Server Checks SPF
    • When an email arrives, the receiving mail server checks the sender’s domain's SPF record.
    • It verifies if the sending IP address is listed in the SPF record.
  3. SPF Authentication Result
    • If the IP matches an authorized sender → The email passes SPF.
    • If the IP does not match → The email fails SPF and may be marked as spam or rejected.

NOTE: This is a basic high-level explanation.

DKIM (DomainKeys Identified Mail)

DKIM is an email authentication method that allows the recipient’s mail server to verify that an email was sent by an authorized sender and that it has not been altered during transmission.

How DKIM Works
  1. Email is Signed with a DKIM Signature
    • The sending mail server adds a DKIM signature to the email’s header.
    • This signature is a unique cryptographic hash, generated using a private key.
  2. Receiving Server Verifies the DKIM Signature
    • The recipient’s mail server retrieves the public DKIM key from the sender’s DNS records.
    • It then uses this key to decrypt the signature and verify the email’s integrity.
  3. Email Passes or Fails DKIM
    • If the email matches the original cryptographic hash → DKIM passes.
    • If the email has been altered in transit → DKIM fails and may be marked as spam or rejected.

NOTE: This is a basic high-level explanation.

Setting Up SPF, DKIM and DMARC

Before configuring DMARC, ensure that SPF and DKIM are correctly set up. There are many tools online that can help you with ensuring you have valid SPF and DKIM records. Setting up the wrong values for SPF and DKIM can impact your email deliverability positively and negatively so be careful.

SPF

Add a TXT record in your domain's DNS settings specifying the authorized mail servers. Here is a quick basic example. Your email provider will give you a more complete example but don't forget to add SPF entries for 3rd party senders that email on your behalf.

v=spf1 include:_spf.example.com ~all

DKIM

Enable DKIM signing through your email provider and publish the corresponding public key as a TXT record in DNS. Your email provider will give you the exact DNS TXT record(s) to be added.

Create a DMARC Policy

A DMARC policy is defined using a DNS TXT record for your domain. The basic syntax is:

_dmarc.example.com TXT "v=DMARC1; p=policy; rua=mailto:reports@example.com; ruf=mailto:forensics@example.com; pct=100"

Once your policy is defined, publish it as a DNS TXT record. Example for a monitoring policy:

_dmarc.example.com TXT "v=DMARC1; p=none; rua=mailto:reports@example.com"
  • p=policy: Defines the action for failing emails. Options are:
    • none (monitor only)
    • quarantine (send to spam)
    • reject (block the email)
  • rua: Address to receive aggregate reports.
  • ruf: Address to receive forensic reports.
  • pct: Percentage of emails subjected to the policy.

Monitor and Maintain Your DMARC Policy

Monitor DMARC Reports

DMARC reports help identify legitimate senders and unauthorized email sources. Use a DMARC monitoring tool or service to analyze these reports and adjust SPF, DKIM, and DMARC policies accordingly.

Gradually Enforce a Stricter Policy

Once you've validated legitimate email sources, move from p=none to p=quarantine and eventually p=reject to block spoofed emails.

Maintain and Update Your DMARC Policy

Regularly review DMARC reports, update SPF and DKIM records as needed, and adjust policies to ensure continued email security and deliverability.

Conclusion

Implementing DMARC enhances email deliverability and security by preventing spoofing and phishing attacks. By carefully configuring SPF, DKIM, and DMARC, organizations can ensure their emails are trusted and reach recipients' inboxes. Start with a monitoring policy, analyze reports, and progressively enforce stricter rules to maximize protection. By following these steps, you can effectively safeguard your domain’s email integrity and improve deliverability.