How To Set Up DMARC For Office 365: A Complete Guide


For businesses utilizing Office 365 for their communications, ensuring email security is of paramount importance. One effective method to safeguard against issues like email spoofing and phishing attacks is the implementation of DMARC (Domain-based Message Authentication, Reporting & Conformance). DMARC allows organizations to monitor their email authentication processes and establish rules that block unauthorized entities from sending emails on behalf of their domain.

This guide outlines a comprehensive process for configuring DMARC in Office 365, which includes setting up SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail)—two critical components necessary for enforcing DMARC policies.


Understanding DMARC, SPF, and DKIM


Before implementing DMARC, it's important to grasp the functions of SPF and DKIM.



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What is SPF?

SPF, or Sender Policy Framework, is a technique used for email verification that enables domain administrators to define the mail servers authorized to send emails for their domain. When an email is received, the recipient's server consults the SPF record to confirm whether the sending server has permission to send messages on behalf of the domain.


What is DKIM?

DKIM, short for DomainKeys Identified Mail, is a method of email authentication that incorporates a cryptographic signature into sent emails. This signature enables the receiving mail servers to confirm that the email has remained unchanged during transmission and that it comes from a legitimate sender.


What is DMARC?

DMARC enhances SPF and DKIM by offering a set of guidelines that domain administrators can utilize to direct incoming mail servers on the treatment of emails that lack authentication. Additionally, DMARC includes reporting tools that assist organizations in tracking email operations and identifying any unauthorized use. For further details, check out www.dmarcreport.com.


Steps to Set Up DMARC for Office 365


Step 1: Configure SPF for Office 365

To set up SPF, complete the following actions:

  • Navigate to your domain's DNS configuration: Sign into your DNS service provider's dashboard.

  • Create an SPF record: If there isn't one already, generate a new TXT record with this content:

    • v=spf1 include:spf.protection.outlook.com -all

    • This record permits Microsoft’s mail servers to send emails on behalf of your domain.

  • Save and implement the SPF record.

  • Check the SPF setup by using online validation tools or the security settings in Microsoft 365.


Step 2: Enable DKIM for Office 365

To set up DKIM:

  • Log in to the Microsoft 365 Defender portal at https://security.microsoft.com.

  • Go to Email & Collaboration, then select Policies & Rules followed by Threat Policies, and click on DKIM.

  • Choose your domain and turn on DKIM signing.

  • If necessary, modify your DNS settings by incorporating the CNAME records supplied by Microsoft 365.

  • Save your updates and confirm that DKIM is properly configured.


Step 3: Create and Publish a DMARC Record

Once you have configured SPF and DKIM, proceed with the following instructions to set up DMARC:

  • Access your DNS provider and go to the DNS configuration for your domain.

  • Add a new TXT record in this format:

v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com; ruf=mailto:dmarc-failures@yourdomain.com; fo=1;

  • p=none: This indicates that no specific action will be taken against emails that fail authentication. You can update this to quarantine or reject after reviewing the reports.

  • rua and ruf: These specify the email addresses where DMARC reports will be directed.

  • fo=1: This option requests detailed forensic reports for any authentication failures.

  • Save and publish the DMARC record.

  • Utilize a DMARC validation tool to ensure everything is set up correctly.


Step 4: Monitor and Adjust DMARC Policies

  • Examine DMARC reports: These documents offer valuable information regarding email activity and any unauthorized access. 

  • Implement stricter policies in stages: 

    • Begin with p=none to gather data. 

    • After assessing the reports and confirming that legitimate emails are properly authenticated, transition to p=quarantine. 

    • Ultimately, move to p=reject to entirely prevent unauthorized emails from reaching your inbox. 

  • Modify SPF and DKIM configurations if needed to avoid false positives.



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Best Practices for Implementing DMARC in Office 365


  • Make sure that SPF and DKIM settings are properly set up before implementing DMARC. 

  • Consistently analyze DMARC reports to identify any possible problems. 

  • If necessary, utilize a subdomain for external email services to avoid authentication conflicts. 

  • Implement policy modifications gradually to reduce potential disruptions. 

  • Inform staff about email security measures and the dangers of phishing.