Office 365 DMARC Policy: How To

Enforce And Optimize It

In the current digital environment, safeguarding email communications is paramount. As phishing, spoofing, and various other email-related threats become more common, organizations need to adopt proactive strategies to safeguard their brand reputation, sensitive information, and users. For companies utilizing Office 365, it is crucial to implement and fine-tune a DMARC policy to maintain a secure email ecosystem.


What is DMARC?


DMARC is a protocol designed for email authentication that assists organizations in protecting against email spoofing and phishing threats. It enhances two established technologies, SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail), to verify the legitimacy of the sender of an email message. 

With DMARC, domain owners can set a policy that guides email recipients on the appropriate actions to take regarding unauthenticated emails, which may include quarantining, rejecting, or allowing them.



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The Importance of a DMARC Policy for Office 365


Protecting Against Phishing and Spoofing Attacks

Implementing a DMARC policy in Office 365 can help mitigate the risk of attackers masquerading as your organization or staff to trick your clients, customers, or partners. A properly set up DMARC policy blocks unauthorized individuals from exploiting your domain for harmful activities.


Maintaining Brand Reputation

When cybercriminals exploit your domain to dispatch deceptive emails, it can significantly erode customer confidence. By establishing a stringent DMARC policy, you guarantee that your domain is reserved exclusively for authentic email exchanges, thereby preserving the integrity of your brand.


Enhancing Email Deliverability

Numerous email service providers (ESPs) favor messages that have valid SPF and DKIM records, so a well-configured DMARC setup can boost the probability that your authentic emails will arrive at their designated recipients. To uncover more, simply click the link.


How to Enforce a DMARC Policy in Office 365


Step 1: Set Up SPF and DKIM Records

Before deploying DMARC, it is essential to confirm that your domain possesses valid SPF and DKIM records. SPF records identify the mail servers permitted to send emails for your domain, whereas DKIM incorporates a digital signature into each email, allowing recipients to authenticate its legitimacy.

  • Configuring SPF: Access your Office 365 admin center and locate the DNS configuration. Insert the correct SPF record into your domain's DNS zone.

  • Configuring DKIM: Within the Office 365 admin center, head to the "Exchange" area and activate DKIM for your domain.


Step 2: Create a DMARC Record

After you have correctly set up SPF and DKIM, you can incorporate a DMARC record into your DNS configuration. This record establishes the guidelines for how mail servers that receive your emails should respond to messages that do not pass authentication. The structure of your DMARC record should be as outlined below:

v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com

  • v=DMARC1: Denotes the version of DMARC being used.

  • p=none: Signifies that the policy is configured for monitoring purposes only, without taking action on emails that fail.

  • rua=mailto:: Offers an email address where DMARC reports can be sent.



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Step 3: Gradually Enforce the Policy

Begin by implementing the "p=none" policy, which serves to observe your email activity without intervening in emails that do not succeed. This approach enables you to review the reports and pinpoint any problems in your email delivery process.

Once you have examined the reports and confirmed that all valid senders are correctly verified, you may adjust the policy to a stricter setting.

  • p=quarantine: Emails not passing authentication are directed to the spam or junk folder.

  • p=reject: Emails that do not pass authentication are completely denied.


How to Optimize Your DMARC Policy


Regularly Review and Update SPF and DKIM Records

Keep your SPF and DKIM records current, particularly when your organization incorporates new services, email platforms, or third-party tools. If these records are outdated, it may lead to legitimate emails not passing authentication checks.


Implement a Strict Policy

After verifying that your authentic emails successfully pass DMARC checks, move towards implementing a more stringent DMARC policy such as “p=quarantine” or “p=reject” to reduce the chances of spoofing and phishing attacks.


Analyze DMARC Reports for False Positives

Consistently review your DMARC reports to spot any legitimate senders whose emails are incorrectly flagged as suspicious or any false positives. Adjust your SPF and DKIM records accordingly to incorporate these senders.